There is no Timer that you can download onto your PS4, and overlay onto a recording or stream(Without using a capture card to stream from your PC). There are two main mobile apps that you can use, “Speedrun Assistant”($1.49 USD) and “FramePerfect Speedrun Timer“(Free). You can also use Livesplit on your computer. It is used by most Speedrunners and is Free. You should also join the GTA V Speedrun Discord, there is a server there for tech support, and I’m sure any future question can be answered much quicker. I hope this was helpful, and good luck on future runs!!