What is the ruling on delaying the break period and using an electric heater to warm food in the office, given that the manager does not object?

There is no harm in delaying the deserved break period if it does not prejudice the work's interest and is with the permission of the officials. There is no harm in using work tools (such as an electric heater) if they are not damaged and are with the permission of the officials, or if their use is customarily tolerated.