I will have to leave for India for a short trip just before the 90 day period.
Can I sign and date my application (95th day) and then my wife send it, say 85th day, to the USCIS?
Do you see any problem with that?
Thanks!
Yeah, this is one of those cases where, on one hand, most likely whichever way you do it, there won't be any problems and, on the other hand, if you are unlucky and get an asinine IO, there could be a problem.
I would not date the application on the 95th day as this might really raise the stink at the interview if the IO notices (otherwise what's to prevent somebody from signing and dating an N-400, say, 200 days in advance and mailing it on the 90th day?).
On the other hand, if the application is dated with 85th day, then all the information contained in the application must be correct as of the 85th day. This means that the trip you are taking just before the 90th day would have to be listed there (but probably only with the departure date and with a blank return date). I think it is OK for you to do precisely that, since I do not believe there is a requirement for you to be physically present in the U.S. when N-400 is filed.
However, since you say that it is a short trip, it is much better to wait until you come back and submit your N-400 then. This will solve all the problems, give you the peace of mind and save you a lot of mental aggravation.