Switch to a sprinter start. No more guess work.
This has been my experience as well. Umpires see movement and it catches their eye.
If the other teams parents aren't complaining that you are leaving early, you are probably leaving too late.
I have my girls imitate the pitchers arm circle and start at 12:00.
#2 is decelerating before she completes her first stride, #42 is decelerating on her 2nd step and body more towards home. Ummm
Last season, our girls never seemed to get a good jump on the pitcher. Our lead offs always seemed late. I created this image for them to see how early they needed to start their lead off.