Etiquette requires that thank you notes are sent within one year of the wedding. This also holds true to gift giving...guests have up to one year to send a gift. Therefore, don't feel pressured to send thank you notes if it is going to cause stress before the honeymoon. The reason to try to get at least some of them out before you leave is just to relieve stress when you come back. I went to two weddings in March. I received one thank you card last week, and I haven't gotten the other one yet, so do what works for you.