[fysiks]

The end-of-map vote should be enabled by default. The vote will come up approximately 2 minutes before the end of the map (assuming the map is set to end at all i.e. mp_timelimit is non-zero). This feature can be en/disabled with the gal_endofmapvote cvar to make sure that it's set to 1.

Make sure that you're game is up-to-date from Valve using Steam and ensure that you're using the official version of HLDS from Valve also.