I’ve been up with DD2 since 5 - she’s 1 (she’s 1 tomorrow) and this is her usual wake up time - between 5 and 6 usually.
DH never gets up early with her and this morning it’s pissing me off so I’ve made no real attempt to keep her quite.
He’s back to work tomorrow so I know he sees this morning as his lie in despite the fact he never gets up with her!
In my opinion a lie in is any time extra in bed after the other person has got up dealing with the kids.