I can't see an issue with this.

Extend your handling time out to cover posting on a Saturday... make it either a 7 day or 10 day handling time.

I would also add in your descriptions that postage days are only on a Saturday due to work commitments. This way you are covering yourself.

Of course they may be people who wish to buy an items from you and need it yesterday! Patience is a virtue...lol! Good luck.