Returning Earlier or Later Than Booked at Birmingham
Coming back off schedule is normal and nearly always fine. The exceptions are worth knowing before you travel.

Airport Guides

The names describe how they are priced, not how far away they are. Short stay is priced by the hour and sits beside the terminal; long stay is priced by the day and sits a short transfer away.
Book the wrong one and the mistake is expensive in a particular way: short stay for a fortnight costs several times what it should, and nobody notices until the invoice.
Hours, not days.
It exists for drop-offs, pick-ups, meetings and the occasional overnight. The car parks sit directly beside the terminal, so the walk is a few minutes and there is no bus.
That convenience is what you are paying for, and the pricing assumes you will not be there long. For a day trip or a single night short stay is often the sensible choice.
Short stay is cheap for three hours and ruinous for three weeks. The difference is not distance, it is the meter.
Days and weeks.
It is the official on-airport option for holidays and longer trips. The car parks sit within the airport boundary but far enough out to need a transfer bus, and the daily rate drops sharply compared with short stay.
For most trips of three nights or more, long stay at Birmingham is the baseline everything else should be compared against.
A few hours — short stay, by a distance
One night — short stay or long stay, usually close
Two to five nights — long stay, with off-airport worth checking
A week or more — long stay or park and ride, with park and ride usually ahead
Three weeks — park and ride, clearly
The crossover point is around three nights. Below it, pay for the shorter walk; above it, the daily rate starts doing real work.
Below long stay on price, above it on effort.
Off-airport sites sit a few miles out on cheaper land, which is why the daily rate is lower. The trade is a longer transfer — ten to twenty minutes rather than a few — and a bus that runs less often overnight.
On a fortnight with ordinary luggage that is an easy trade. On two nights it usually is not, which is why the same advice produces different answers depending on how long you are away.
No, and at Birmingham it is shorter than at most UK airports.
The single terminal means the official car parks sit closer to the building than at a sprawling multi-terminal site. You are walking to a bus stop within the car park, and the bus does the rest — usually under ten minutes door to door.
That proximity is why Birmingham's long stay competes more closely with off-airport than it would at Heathrow, where everything is further apart.
Considerably.
There is no terminal to confirm, no risk of booking against the wrong one, and no inter-terminal transfer. At Heathrow and Manchester that is a genuine source of error; here it simply does not arise.
It also means every car park serves the same building, so the only variable is distance and transfer time.
They are different things entirely, not more car parks.
With meet and greet you stop at the terminal, hand over the keys and walk in. Valet parking is similar, though at Birmingham it often means the car stays in an official car park rather than going off-airport.
Both buy you the short-stay walk at something closer to a long-stay price on short trips, which is why they are worth pricing on an overnight or a weekend.
Work from the length of the trip, then check the time of day.
Under three nights, short stay or meet and greet. Three nights to a week, long stay. Beyond a week, compare long stay against park and ride and expect the latter to win.
Then adjust for an early departure or a late return, where the shortest transfer you can afford is worth more than it looks on paper. The comparison prices all of them for your actual dates.
Short stay is priced by the hour and sits beside the terminal. Long stay is priced by the day and needs a short transfer.
Only for a day trip or a single night. Beyond that the hourly pricing makes it far more expensive.
Usually under ten minutes door to door, shorter than at most UK airports thanks to the single terminal.
No, which removes the terminal confusion that complicates parking at Heathrow and Manchester.
Generally from about a week upwards, when the lower daily rate outweighs the longer transfer.