Thumb sucking-

How long self soothing whilst sleep training is okay. It’s a weird question I know, my LO sucks his thumb a lot now to self soothe sometimes continually for about 40-50 minutes to keep himself calm Is that too much? He’s been fed and checked but that’s how he puts himself to sleep. He’ll sleep like 30 mins then wake up and start sucking his thumb again.

So how long is too long?

Is it bad for his skin/nails?

My in-laws keep telling me horror stories (their kids have pacifiers)