vTaskDelay(1) will delay the task until the next tick occurs, which might be just moments later, or might be up to the full period of a tick.
vTaskDelay(2) will delay the task until 2 tick occur, if the first one occurs very quickly after the call, the delay time might be just slightly over 1 tick in length.
This is due to the granularity of measuring time in “ticks”. The whole period from the nth tick until the next tick occurs is consider to be the time of tick n, and that jumps to n+1 when the tick interrupt occurs.
You need to take this fact into account when making short delays.