Sorry for the long post...
We started about 4 weeks ago with our now 22mo. Got poops straight away, nearly all have been self initiated. But he doesn't seem to get it with wees.
We've never really had fights with him to go for a wee, if I prompt he'll go. Or if I take him as a toilet buddy and bring the potty sometimes he'll self initiate and sit on the potty for a wee without me asking.
If he drinks a decent amount, he'll tend to go after an hour. But has been able to not wee for 2 hours. If I'm focused, I'll spot his sign which tends to be grabbing and looking a bit uncomfortable. If he wees in his trousers, sometimes he'll say 'hold it' as I said that once aha. And if I do catch him mid wee, he can stop and hold it to them finish in the potty. He knows when he's weeing, so if he's having an accident he'll look down and tell me he's weeing for example.
But generally, his wees aren't self initiated. It's me keeping an eye and prompting. Did I start too early? His speech is great so he can communicate. He has a potty book and he told the boy 'next time potty' when he had an accident.
He had a fairly positive weekend of self initiating a couple of times, but he's still having at least one wee accident every day and today was chaos with 3 wee accidents and 1 poo accident (it was a busy day and I wasn't as on it with the prompting). I did loosely follow the Oh Crap method.
I don't feel like I can go out for long or far!