Could you tell us some of the details?
When negotiating anything, both parties are usually trying to reach a settlement that's satisfactory. If I'm right, you received a contract (I assume that's what you mean by "offer") from a publisher and you're not satisfied with some of its terms....you've been negotiating hoping to reach acceptable terms -- right? Given yur question, I also assume you don't have an agent.
You ask, "... what is the time they expect you to sign for?" and "What is the industry standard." There's no absolute standard, although publishers certainly expect that you'll sign (or not) after you and your intellectual rights attorney have a week or two to review same. If you want changes, they expect you tell them a/s/a/p. If it were me, once I received the contract I would immediately acknowledge its receipt. I'd thank the editor and tell her that I need a few days to read it over and review the details ("I'll get back to you in a few days--a/s/a/p"). After reading the contract and making notes I'd contact and meet with an IR attorney a/s/a/p (if you're published consider the legal department at the Author Guild). Don't rush, rush, rush --- but don't lag, lag, lag.