You’ll be fine as long as the specific BA desk is open, e.g. if they’re also checking in for an earlier flight. It’s not staffed all day but opens 2 hours before each flight and will close if there’s a longer gap, so check the schedule. Alternatively, if your ticket allows FCOD you could change to any IB flight, in which case you can check in and drop bags at any point during the day (or even the night before).