How long of a period do you think there should be between the time someone's spouse dies and the time they get a new boyfriend or girlfriend?

I thought of this because a woman that I know recently died. She was in her mid 40’s and she had cancer. She died in mid October and it is now beginning of January, so it’s about 2½ months. Her husband just wrote on his FB something about having a girlfriend. I am kind of surprised that he got a new girlfriend so quickly.

I know that people do what they feel is best for themselves and don’t worry about others’ opinions, so I am not here to be derogatory about this person’s actions.

I am wondering if you think there is a certain period one should wait before dating a new person after one’s spouse dies?