T1 and T2 are two individual timer settings that allow you to set two separate temperatures during a 24 hour period. For example: T1 can be set to 72 F (22 C) during the morning hours of 5 AM to 9AM, and set from 6PM to 5AM at the same 72 F (22 C). T2 can be set to 66 F (18 C) from 9AM until 6PM while you are not home. This example is showing how you use two separate temperature settings during a 24 hour period. 
*Please note: T2 is always used for the lowest temperature setting*