1. Copy "zm_timemachine_v1fixed.bsp" in your "csgo" folder which is located in your Counter-Strike Global Offensive folder.
i.e: C:\Program Files (x86)\Steam\SteamApps\common\Counter-Strike Global Offensive\csgo

2. Start CS:GO, open the Console with the key above Tab and type in "map zm_timemachine_v1fixed"

3. Play and Enjoy! :D