Stakes, once delegated, do not become effective immediately. They must first pass through a warmup period. During this period some portion of the stake is considered "effective", the rest is considered "activating". Changes occur on epoch boundaries.
Warmup: When sending a staking transaction to the network, stake first needs to activate before it influences the consensus process and begins to earn rewards. The time this takes is dependent on how much VLX is beginning to stake relative to the VLX already at stake. Up to 25% of the VLX already at stake can warmup per epoch and start to earn staking rewards.
In the best-case scenario, when a reasonably high percentage of VLX is at stake and there is little new stake entering, this will usually mean that stake will become active in the upcoming epoch that the staking transaction was sent. In times of high stake turnover, e.g. at network launch, stake will progressively activate meaning that only a fraction of stake will enter the validation stage each epoch.
Cooldown: When deciding to stop staking, staked VLX needs to pass a period during which stake remains eligible for penalties before it becomes liquid.
Similar to the warmup phase, this happens gradually and works in the same way that warming does,
with a maximum of 25% of the VLX at stake being able to pass the cooldown phase per epoch.