I’m well aware of the difference between ‘since’ and ‘for’. However I have a doubt: Imagine I say ‘I’ve been working on the essay since Saturday’ or ‘I’ve been working on the essay for two days’ (correct right?) Why would it be incorrect to say ‘I’ve been working on my essay for all weekend’. I would personally omit ‘for’.. why though? Thanks

I’m well aware of the difference between ‘since’ and ‘for’. However I have a question.

Imagine I say ‘I’ve been working on the essay since Saturday’ or ‘I’ve been working on the essay for two days’. (correct right?)

Why would it be incorrect to say ‘I’ve been working on my essay for all weekend’? I would personally omit ‘for’, but why though?

It seems like you can also omit the proposition in other, related cases, like 'I'll see you on Friday night.' Again, why can you do that?