In this talk I will present the CMS High Eta Upgrade project which aims to install Triple-GEM detectors instead of Resitive Plate Chamber (RPC) in the forward region (1.6<|eta|<2.1) of the CMS muon sprectrometer during te 2nd LHC Long Shutdown (LS2). Then I will focus on the Time Over Threshold (TOT), a fast method to measure the arrival time of muons in the detectors and to assign the muons to the correct LHC BX.