He's got an unpredictable schedule.
He can go weeks without seeing her.
But one of the rules, one of his rules, one we agreed to, is that she's his when he wants. Sometimes he schedules a date with her weeks in advance, sometimes he calls that day.
But Emily and I should be able to plan, of course, so we have a shared google calendar where he can see the times she isn't available, either because of work or other obligations. They are color coded, of course. Brown for her work events, blue for her personal events, pink for special time with me, orange for everything else.
He respects the pink, but orange is fair game, even if she has "non-special" plans with me.