[gruez]

I'm not sure I follow here. The transaction might be structured as the landlord giving you 12 months of housing service at the time of signing of the contract (or when the lease starts) and you paying him in installments of 12 payments (with the first one or two upfront), but you don't "take delivery" of the service all at once. It's given to you on a continuous basis. Therefore, at any moment during the 12 months, you don't owe the landlord anything.

[syshum]

The second you sign the lease you owe the landlort the full amount. It is a debt you owe.

Does not matter if you realize the use of the property or not, for example if you signed a Lease on an apartment in January, then due to a global pandemic you could not move (through not fault of the landlord) in until July you would still owe the rent for the 6 months even though you did not occupy the unit.