small press open reading period, how long for results?

If they didn't state any guidelines I'd wait 3-4 months.

How long is a piece of string? It depends on a lot of factors such as how many submissions they get, how many staff they have working on those submissions and so on.

Duotrope's digest has a useful feature which gives average response times for most of the publishers in their database, based on the times writers report for them. You can use this as a general guide. However, there is a great deal of variety. Some respond within a month, others (Tor.com, for example) state on thier submissions guide at least 6 months.

A lot of people who submitted work to Angry Robot (not a small press, but still an open door period) at the beginning of March are still waiting for a reply. I agree with areteus - you need to wait at least 3-4 months.

Did you get an acknowledgement of receipt? If not, I think it's not unreasonable to send a polite email after 3 months just to confirm that much. I've heard zero back from one agent who isn't a "no response means no", so I'm beginning to think he never got it (I since signed with someone else, so I didn't bother nudging).