Possibly unpopular opinion: I do expect you to answer me whatever day of the week it is. You have a smartphone, and I know the connectivity apps work on the weekends, too. Having said that, you have every right to expect me to be judicious in when I ask you to respond.

Bottom line: it’s on me (as the boss/co-worker) to not abuse the privilege. But you have the responsibility to respond when I deem it needed.

Honestly, because that’s what the (salaried) money is for.