Is it obligatory to pay the sustenance allowance when there is a surplus after working hours, or can it be left for the next working day, or disposed of?

The partnership between you requires each individual to pay a specific amount for your sustenance, and whatever remains is yours. Allah's saying, "So send one of you with this silver coin of yours to the city and let him see which of them has the purest food [and bring] you provision from it" (Quran 18:19), indicates their partnership in the price of the food and, consequently, in the food itself. Therefore, you must pay your share to be entitled to participate in the sustenance and its surplus; otherwise, you would be consuming their wealth unlawfully. Allah has forbidden this, as He says, "O you who have believed, do not consume your properties among yourselves unlawfully" (Quran 4:29). And the Prophet, peace and blessings be upon him, said, "All of a Muslim is sacred to another Muslim: his blood, his wealth, and his honor." Their silence does not permit you to do so, because what is taken out of shyness is like what is taken by force.