Ok, I think I understand what are your needs.
So there are several things here that would be possible to add :
The ability for the user on the checkout to select whether it's a one time payment or a recurring payment.
If it's a recurring payment, the ability to choose a frequency. Maybe a starting day ?
handling recurring payments with paypal.
the ability to choose a delivery time period for the day of the deliveries. (that can already be done with custom fields in hikashop)
when a recurring payment is received from paypal, generate an order instance and send an email to the user (for information) and the admin (so that he can do the delivery).
The possibility to choose the frequency with multiple days in the week would complicate the frequency selection but more importantly, paypal can only handle recurring payments if the frequency is simple : every 7days, every 2 weeks, every days, every month, etc. It cannot handle mondays and tuesdays.
Also, it's paypal which handles the reccuring payments once the first order is validated by the user. So HikaShop cannot trigger paypal to process the payment after the goods have been delivered.
All in all, that is quite a lot of stuff to add to HikaShop to make it work and it won't be exactly as you want.
Recurring payments is something we want to add to HikaShop, but really in the long term (6 months/1 year).