If we get in a taxi right now, we might still make it on time.
Sorry! I'm stuck in traffic, so I'm most likely not going to make it to the appointment on time.
"Do you think we can make it in time?" "Well, it’s almost seven o’clock. Do the math."
There is an interval (of time) that you need "to suit" (合う). To suit that interval, you need to be there before the time in question. That's why this word means to be in time for, to make it on time or to be on time for.
You learned this reading for 間 when you learned 間もなく. And the reading for 合う is just that of the word 合う. If you remember them both, you'll remember this word!