This idea sounds great!!
Do only certain parlours do this, or is it a case of ringing and asking any parlour if it's an option.
I think most would, so long as the girls are happy to work together.
You would just for example have to book:
Girl A for 45 mins at 5pm
Girl B for 30 mins at 5.30pm
It could be a bit of a pain if Girl B gets a walk-in at 5.05pm, or a 5pm is late ..... Roses are great at sorting stuff like this