I have a team of 3. I asked one of my team members (A) to support a new member of staff with a specific task which was new to her. The task involved doing some work for B - not part of our team. A then told me that as she had to work outside her usual hours, she had agreed with B to take those hours as TOIL, and asked me if she could go home early on a specific date. A does work extra time regularly (on an entirely voluntary basis - no TOIL involved) and I didn't want to be petty, so I agreed to the date she requested. She did say the date she's asked for was convenient (teenage DC's birthday) rather than critical. The date is next week.
Since then, one staff member has been signed off sick and the other has a hospital appointment that afternoon. If A goes home early, it will leave me dealing with callers and other interruptions etc while trying to complete a time-critical project.
I am hoping she will realise the situation and offer to delay it: any other day would suit me but obviously she can't change the date of her DC's birthday. Can I insist that she takes her TOIL another time or should I honour the agreement? HR policy is silent.