How do I make something repeat every x second as a action?

If for example you are using the 8Direction behaviour, this is the simplest way to add speed. Create a Global Variable called Speed and then every X seconds, add value to your speed, and then set the maximum speed of the Player.

That's not a good solution, because if you press+release W key repeatedly roughly once per second, the speed will still increase.

If you need to increase the speed by 10 for every second the key is held continuously, you can do this:

Global variable startTime=0

On W pressed: Set startTime to time

On W released: Set startTime to 0

On every tick
startTime>0 : Set speed to initialSpeed + int(startTime)*10

Oo nice I see. didn't take that into consideration.