unblock slots from the cart

Hi,

is there any way to unblock time slots that are blocked in the cart?
Let say client starts the booking, select day / hour and service, adds to the cart and goes away. If you check in other browser, this time slot will be unavailable.
Can this time slot be somehow enabled ("released") in the joomla's administrator?

Another question related: can you limit clients to add just one item to the cart? I can see just an option "Prevent registered user from booking more than one timeslot per date", but this is not what I mean.

Thank you for response in advance.