You'll feel it when it's time, that's really the only way lol

I told my first ex I loved them before we started dating, don't recommend that. Told my most recent ex I loved them after she said it to me first, and it was probably too early at a couple months and a handful of dates in but I was fine with it - I had wanted to say it earlier than she did.

I dunno, you just feel it. There's no like guide or whatever. It's like trying to describe what being sad or being angry is... you just feel you're in love and the time you say it is probably going to be the right time.