As Szymon says, you have not given an appropriate example: In your sentence でも is being used to give two options but で can be used to indicate when something finishes or a duration:
-> finishing time:
My work finishes at 5pm.
You could also use に but whereas に is a more general particle that gives the time at which an event occurs (ie when work finishes) the で places more emphasis on the time an activity lasts for.
無色受想行識 wrote this report in three days.
You have not asked about use of に so I assume you know it is not used with all temporal expresssions but, for reference, the general rule is that if the time can be specified with a digit then に is used (eg Xmas day is 25 Dec -> クリスマスに）
Reference: Dictionary of Basic Jpse Grammar