You should give plenty of notice before cancelling plans.
Yuri has planned a vacation with a friend which is about 3 months away and has just found out she has to attend a work function during that time.
Yuri wants to let her friend know she can't come.
Yuri lets her friend know that she cannot go with her as soon as possible.
Yuri waits until a month before the vacation to break the news to her friend.
Yuri's friend has plenty of time to make changes to her plans.
Yuri's friend has already made arrangements and has to go alone or lose money.