Definitely will be trial and error.

I'd you have time I would do a full pump at 4 as you will continue making milk and should be able able to give a full bf by the 6pm feed and if he fusses you could Offer some EBM. Some babies do feed more often when you are around and take less EBM when you are away so be prepared he may do this

Good luck expressing and working c. An be chaos nick but is worth it if you can keep it up