-If you mean, "when is the best time to mail out to seniors concerning their senior portraits?" then, july and august before the senior year starts is the best time (actually, this is just when all the photo companies put out there stuff, so if you want to keep up with them, then...)

-1. TARGET YOUR SCHOOL
2. Select 3 or 4 of the campus top students (athletes) (most popular)
(class officers), etc. Give them comp sittings and wallets for payment to use their pics as promotional material.
3. Hire one or two girls from the target class to make up the mailing list. Usually twenty to twenty five cents per name will get you a complete list.
4. Design and print your promos in January or February It's comprised of a two piece promotional program. An early mailing (March) lets them know you are in the Senior Portrait Business.
5. Get a foot in the door so they can familiarize themselves with you. Shoot a school dance, Grad Party, Prom, or what ever. Do the damn thing for free if you have to.... just get in there. Put your flyers in the picture packages you distribute from these events. Also build your "prefered" customer list
6. A second mailing (early June) sets hook with your specials. That should keep you busy in July and August.
7. Be sure to get the yearbook dimensions from the yearbook advisor.

8. I hope you don't live in Sacramento, I may have just created a monster.