making a lawn

[UntamedWisteria]

I've hired the rotavator, and will be doing this later today.

Most advice says you should then wait a week for the soil to 'settle' before sowing seed but I'm aware I've left it all quite late in the year.

Will it make a difference if I just press on and sow the seed today as well?

It's really not that late. If you talk to a green keeper at a Golf Club, you'll find they sow grass all year round. It just grows faster when the soil is warm. We've got some amenity area grass seed that takes 4 weeks to germinate, even in ideal conditions!