A friend of mine is starting a new job in a few weeks. The contract is already signed.

The manager just send her an email in the morning asking her to do some work until next day.

She currently has a another job and the manager knows this. It looks like a lot of work - it will take at least several hours, maybe even a whole day.

She doesn't want to start on bad terms by rejecting the request. On the other hand she won't get paid for this and would need to work the whole night (or at the weekend if she asks for more time). How should one react in such a situation?

Update

She talked to her manager and he tried to downplay the whole situation. He said that he wasn't really expecting any results and just wanted to ask her nicely if she maybe had some time to analyze a document. But in the email he forgot the part about asking nicely and wrote something like "I know you don't work for us yet, but please do this" and attached several hundred pages without mentioning which parts were relevant. The task was still way to big and simply not the kind of task that will get you any meaningful results when rushed or without carefully reading everything he had send.

Another Update

In conclusion everyone saying that this was a red flag was absolutely right. Management at that company was really bad and quite a mess, which reflected in their employees general bad mood and morale. I didn't help that she was direct subordinate of two chief officers, which both tended to frequently give her large task with unreasonable deadlines. She left the company after some month.