Diary Format

Standard first person allows you to write about things happening to the characters in the moment. Diaries, however, talk about things after the fact--maybe things that happened earlier in the day or the week. Because of that, the sense of immediacy is different. When people are busy running/fighting for their lives, they don't stop in the middle of the action to write it down. Instead, you build suspense by playing up everything that happens leading up to the action and then have a gap in the diary entries for when the action actually occurs. Since you have multiple POV characters, you can fill the gap with another character's diary entries, leaving the readers to worry about the one character that has stopped writing. This is just a suggestion, and I hope it makes sense because it's late and my brain isn't fully functional right now.

Agreed with Morning Rainbow.

A diary is sort of like a letter, be it to your future self or a loved one (some people keep journals/diaries in this format, actually); instead of narrating events as they happen, you're writing them down at a time when you can pause to reflect. This allows you to both distance yourself a little and delve a little deeper into your thoughts as you reconsider and recollect and maybe make connections you didn't see as things were happening. (As a quick bad for-instance, a fight with your brother is, at the time, a heated exchange of words leading to an angry decision to cut him out of your life. In the diary, perhaps written a day or two after the fact, you might recall how you used to get along with your brother, or realize what triggered your anger wasn't the fight at all but some other frustration, or you could express regret because he gets in a car wreck shortly afterwards and is now in a coma and you may never get to make amends - none of which would be obvious tangents to follow in the heat of the argument itself.)

My Confessions universe is written in a journal-like format, albeit from a perspective a lot farther down the line than a week or month (Psycat's first entry is technically written 3 years after she received her powers, and can be considered a memoir of her story). There should be a bit of memory fade, but also introspection on events in my opinion.

Epistolary novels were the origins of the modern novel format. They are a super-exciting genre because it is so apparent that the only place the complete story resides is in the mind of the reader and writer. The written artifact is incomplete without the work done by the reader to tease out causality and connections between characters and entries. Then you also have the issue of how well characters know themselves, how skilled they are at observing, etc, that adds a layer of interpretation to processing each entry. Of course, now we have a transactional theory of reading that extends this insight about where the story resides into all stories, but I still think it is most apparent with the epistolary format.

One way to mix multiple diary entries is to present the diary alongside commentary by someone who found it later down the line, like an academic. You can also include other 'found' documents like newspaper articles and the like, as this person tries to accurately document what happened.

There was a book called "Pale Fire" that did this. It consists of a long poem and commentary by an academic who knew the author, but it becomes apparent the academic is full of it and injecting his own ideas into the mix.

It might also be a way to hint that the apocalypse or whatever had a happy ending.

I agree with a diary, it's a lot harder to writer with a sense of urgency. You know the narrator at least made it out okay, because they are feeling well enough to write this entry.

You might be able to create more a sense of suspense by playing with the formatting itself more than the actual narrative. create places where the author stopped suddenly, or in blots or tears in the page. If you want to create tension in the narrative, maybe write an entry in short sentences with a lot of spelling errors, conveying that the author was in distress and not thinking clearly when they wrote it.

I know that your issues were resolved above, but just thought a few more examples that you might not have come across could be useful! Especially if you're trying to write diaries of multiple characters who would write their diaries very different ways.

- I Capture the Castle (pretty classic novel) - captures the narrator's gaze/world view, and also manages to describe their world while formatting in journal setting, including how the world adjusts in response to the process of her writing the journal
- Code Name Verity (YA historical fiction) - first half is written in diary (well, confession) format, also interesting twists in second half using the format
- The Enchanted Chocolate Pot by Patricia C Wrede and Caroline Stevermer (MG/YA fantasy) was written exclusively in the format of letters - they actually wrote the first draft that way, writing eachother letters back and forth.
- We Need to Talk About Kevin (modern adult fiction) - good example of how diary/letter format looking at past events can conceal an unreliable narrator
- Bridget Jones Diary (modern adult fiction) - the classic, also a good example if you're thinking about how different people would write a diary - what do they write down? what do they track? when do they write, when do they not?

Very different books, very different perspectives and diary styles, so hopefully something will be helpful. Good luck!

Writers who used the Myth of Cthulhu wrote some their stories like diaries, including Lovecraft (short stories). To give a few:

The dweller in the tomb - Lin Carter (As the story advance, the MC loses track of the time as well as his sanity... sorry, Myth of Cthulhu imply someone losing his sanity.)
Out of the ages - Lin Carter (The last part is a police report. The police report gives the conclusion to the story and what became of the MC, or at least what is known from an other point of view.)
In his daughter's darkling womb - Tina L. Jens (Alternate between diary entries and direct action)

One advice: Avoid diary entries written while the action takes place and ended with something like "Oh god! They are coming through my door but I must write until the end while something terrible is happening to me!". I exaggerate a little, but I don't find this really credible. If some terrible creatures were to enter my house, writing what is happening would not be my reaction.