It varies for a number of reasons. Probably since you are early, expect a few weeks or so.
My DS received an loa in December. He was one of the early ones for the class of 2019 as we could see acceptances on the parents page for 2019 students after they accepted their appointment. He received his appointment early January after paperwork from Dodmerb, and nomination were finalized. Although we knew they all were coming. Congressman called to tell him on Christmas Eve. Best Christmas present!! One thing DS learned through the process is patience really helps. Good luck and best wines as you work toward n appointment to the class of 2020.Or not accepted....
According th admissions, the bulk of responses will go out starting mid-March. Many at that point will be put on Hold and some won't get the final word until early May. If you are one of the few to get an LOA, please don't sit on it any longer than necessary. Around that March-April timeframe, the quota from your state gets filled and everyone goes into the nationally ranked (instead of state ranked) pool. If you decline your appointment after that timeframe, it opens up a national spot, but it is no longer reserved for your state.
If you are a top notch candidate then you should get a LOA soon if all you stuff is in. (Nomination, medical, CFA excluded)After you complete the whole application and the portal shows no more missing documents, how long does it take for you to find out if you are accepted?