Are we allowed to use the "fast craft" when doing a Minecraft Speedrun?

I have watched people like Dream speedrun Minecraft and I am a big fan of Summoning Salt's videos. I want to start speedrunning Minecraft 1.9- 1.15 just for fun and not extremely competitive (even though I have never beaten the game lol) If you have any beginner tips please tell me them because I am clearly inexperienced.