How long would it take for an alien civilization to populate an entire galaxy?

Let's say there are aliens out there.

Let's also say that they are slightly more advanced technologically than we are. So, they can build ships of some kind that either a) have AI that can self-replicate if they find a planet with materials to build more probes, or 2) carry aliens with them that can settle* a suitable planet they find. They then establish themselves, grow, and send out more ships when they are capable.

How long would it take for them to populate the entire galaxy?

It's an int...