The owner should have the faculty to select default options for delivery (ASAP or timeslot) that should be displayed to customer. Also if you modify:
you obtain the timeslot as default option.
With the previous modification once the opening time of the venue has passed, even if no time slot is selected, it is possible to proceed with the order. The order time will be given by the current time plus the preparation time. It would be preferable not to have any slot pre-selected by default, but to make it mandatory for the user to select it.
After modification, visit the store page at a time when delivery is active (NOT before); at this point, without selecting a time slot, it will be possible to complete the order. An order will arrive at the restaurant with delivery time given by the current time plus the lead time.
What do you think @sampoyigi ? Can be useful to others too?