Hi, I want to start speedrunning on console but I do not know if i need to have an on screen timer in the run and how I would get the timer on ps4 if I needed to have one.

You need to check the rules of any games to find out what their requirements are for submitting runs.

The vast majority of console leaderboards will not require an onscreen timer, but of course, as was mentioned, check the rules before you record your run.