They have a contractor who is there ready and waiting to do a job, with all the equipment to hand, and that contractor is to complete by a set deadline ahead if the summer schedule. They wouldn't have been able to do anything Thursday night due to the weather, so doing nothing again last night would probably put them behind schedule.
Effectively, when you have a contract, the runway becomes the contractors at a set time. If the airport stops this and the works overrun as a result, the additional work required to complete, can be viewed as out of contract and frankly, will cost a fortune. It's ironically known as 'Dayworks' and is a licence for contractors to print money..In the same way, if the contractor fails to meet the target, then LBA will be compensated under the contract terms. So, LBA telling contractors to just hang on a couple of hours while late aircraft get in, really isn't an option . ATC cover will also be planned around the published hours.
All airlines were notified of the night closure ahead of the winter period and know that if they are late, for whatever reason, they will be flying elsewhere. It's the same at any airport with a single runway.
Regarding the conditions, as long as their were runway slabs accessible to replace, which clearly there were as the runway was in use, then the contractors can work.
Please see my explanation above.