Cliché: jump the gun

Meaning: get out ahead of the official start. Origins and uses.
Rewrite 1: beat the whistleⁿ⁵
Rewrite 2: lead the starting pistol
Rewrite 3: start without the refereeⁿ²
Rewrite 4: push the stopwatch*
*This one is a little less clear since it's a "stop" watch and not a "start" watch. You could use "timer" or "official clock" but you would probably have a similar challenge.

Comment: This one needs some sense that you are launching or starting ahead of the agreed official start time. It isn’t about being "ahead of your time."

More reading about clichés
What I found when I googled “clichés”:
• Book of Cliches – “Phrases to say in times of trouble.”