If it's the Harlequin Steeple Hill, then Writer's Market should have the response time listed. There will be a copy in your library's reference section.
I couldn't find info on turnaround on the website, but I'm pre-coffee.
For a large house like HQ, then anything from 6 weeks to 6 months is the norm. If they say "6 weeks" double that time. It'll be more accurate.
If you didn't put in a SASPostcard with "Your MS (title) arrived on ___ at Steeple Hill" for the editor to drop in the out box, and you are worried that it never arrived, then a brief query is ok.
After about 6 weeks, you can send a snail mail with "I'm inquiring about the status of my MS, (title) that I sent in on (date). Did it get there? Thank you, ___. Put in a SASPostcard with a yes/no to circle on the reply side. Don't make them write you on their own.
This presumes your MS is not buried under 200 other MS stacked on the editor's desk that she has yet to read. Take it as a certainty that it IS.
I've had my MS on my editor's desk since last October--my 22nd book with her, so we're not strangers--and she's only gotten to it this last week! Six months I've been waiting--and I have an agent and a track record with this house!
Publishing is slow. Keep your head from exploding. Have your next book finished and ready to sell to them by the time they get back to you.
It's what I'm doing.
Good luck!