Seats are available daily, but with a deal this good, there's only scattered availability left. So you'll need to be flexible with travel times. Fares at this price can be found starting in early January through the middle of February. Other dates are available in the same travel window for a few dollars more depending on the connecting airport and inventory.
Some departures may require a long layover so take note of that while booking. As an example, I found seats departing BWI on Tuesday, January 22 and returning from MBJ on Thursday, January 31, 2019.
If Jamaica isn't for you 'mon, then have a look at flight to other destinations across the globe on our Baltimore (BWI) flight deals page.
Need a room near Montego Bay? Hotelwatchdog has a list of available places by the beach for the mentioned dates here.