How long can sessions be for my 12 and under swimmers?

Under Article 205.3.1F, except at championship and open water meets:

• Events for swimmers 12 and under must be planned to finish in 4 hours or less per session (prelims, finals or timed finals).
• The same 12 and under swimmers are limited to one session per day. At prelims/finals meets they can swim one prelim session plus the related finals.

Development competitions (205.11) are for athletes 12 and under. Their sessions are capped at 2 hours, and each athlete swims in only one session per sanctioned competition. Events come from the development list: 25s and 50s of each stroke, the 50 and 100 free, the 100 IM, and 100 or 200 relays.

When an age group meet runs over two weekends, the younger age groups must compete on the first weekend (205.2.3).