Submissive squatting does not involve / need any contact with the birds. It can happen when you approach them. At the end of the day, they will lay when they are good and ready - frustrating, I know.
ETA: here's the link - https://www.backyardchickens.com/t/297632/silkie-thread
Hello and welcome to BYC. I'd guess it varies as much with any other breed. Once they begin submissive squatting for you, you know that its not too long to wait. There's a silkie thread you may wish to check out - the search box will help you.
Best wishes
CT