In order to vote, you must lock your CVX tokens for a fixed time period(a minimum of 16 weeks). Locked tokens will be inaccessible until 16 full epochs have passed.
If you lock immediately before a new epoch starts, your CVX will be locked approximately 16 weeks.
If you lock in the middle of an existing epoch, your CVX will be locked for 16 weeks + the time between your lock and the next epoch start.
Locks are grouped into weekly "epochs" which start on Thursday at 00:00 UTC. Deposits during the current epoch do not count towards currently active vote weight. CVX must be locked in a completed epoch prior to a vote starting in order to participate.