What's the etiquette here ?

[EttiketStriker22]

I'm going out with some mums from my DS school at the weekend.

I'm driving and I have offered a lift to a couple of the mums ; slightly out my way but I don't mind .

I have plans for Sunday morning so I don't want to be out too late .

WIBU to just leave when I'm ready and offer the mums a lift back at the same time , or am I supposed to wait around until they are ready to go ?

Tell them in advance you are happy to pick them up but can't offer a lift back unless they want to leave at the same time as you.

You need to let them know that you'll be leaving early so they can think about what they are going to do before you all go out

Ok if I tell them in advance , is it rude of me to leave and give them the choice or should I be staying til they want to leave ?

Tell them in advance you are happy to pick them up but can't offer a lift back unless they want to leave at the same time as you.

This^
Easy

If you warn them you are going to be leaving earlyish it isn't rude at all to leave when you want to. You don't have to stay later for them.

Different if you just offered a lift and then suddenly sprang it on them that you were leaving.

You're the driver, you leave when you need to.

If you offer a lift just say 'happy to drive back too, but I will be leaving earlyish, by xx o'clock just to give you a heads up'

As Damn says, just factually name the time you are leaving and then they can make informed decisions about what they do. And, you can relax and enjoy yourself.

Definitely give them a heads up in advance but YANBU to leave when you want to