Use this phrase to talk about the one important element of a situation or skill.
For example, imagine that you hid your daughter’s birthday present in the closet. Your wife says that she will certainly find it:
She’s definitely gonna find it. It’s just a matter of time.
In this case, everything is ready for your daughter to find the present. The only question is time, or when she’ll find it.
If you’re getting ready to host a big party, you can say to your friend:
Okay, we’re basically ready. It’s just a matter of how many people are coming.
In this case, you are completely prepared; the only thing unknown is the exact number of guests.
If you’re arguing a lot with your boyfriend, but you know you just need to communicate better, you can say:
It’s just a matter of communication.