As a general rule, Thumb-2 instructions are executed with timing constraints identical to their ARM counterparts. However, there are some second order effects to the cycle timing that you must observe. First, the code footprint is smaller, which can reduce the number of instruction cache misses and therefore reduce the cycle count. Second, branch instructions tend to be more densely packed, slightly reducing the branch prediction accuracy that is achieved and therefore increasing the number of branch mispredictions. Neither of these effects can be accurately measured using hand calculating techniques.
The code footprint and densely packed branch instructions can have an impact on the performance of the processor. In most cases, the interaction of these effects might cancel with each other.