A method and system for synchronized switching of a Transmission Time Interval (TTI) between at least two different TTI length values. A UE 100 transmitting a power report, where a control node 150 or a Base Station 110A evaluates the report and decides, based on the evaluation to order the UE to switch to a different TTI length. The order message comprises the number of TTIs after which a TTI switch has to occur, composed a.o. based on radio environment condition. The UE receives a TTI switch order message and replies with a single message to its serving BS with a message to switch the TTI in a synchronous way.