90 days won't get you to 4/15. You'd need a 120 day lock, and even then with the upcoming rainy season I'd recommend a longer lock in case the builder runs into a construction delay. Wells has their "Builder Best" which is a long term rate lock option. Ask about that, see how a 30 fixed lock might look under that program and decide from there.
I've long been under the impression that the US recovery is really no more than a manufactured sugar high, derived from cheap debt, disregard for stock fundamentals, and tech obsessed consumerism. We're overdue for a diabetic like shock to the system, because as we all know actions still do have consequences. If we do see a 2000-3000 incremental DJIA drop my guess (and that's all this is....) is that we'll still see 3.x rates for some time. Talk about lower or higher rates is just that - talk - so if you sleep better at night knowing a 3.75% rate is locked in with an option to float down if terms improve, it's $700 well spent. If you can stomach a few up and down days, wait.
My .02c
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