I assumed you model a bus stop at an intersection in VISSIM, and the bus is not on a dedicated lane. In that case, there will be immediate traffic delays due to the queue of vehicles waiting behind the bus (for passengers alighting and boarding). You can set how long the bus has to stop by using the stop sign feature and adjust the time distribution as desired.

Hope it answers your question correctly.

There is a 'Stop Sign' feature in the Network Object list (on the left side of the screen). You can place it in the area where you want the bus to stop for alighting and boarding passengers. Then, the time distribution can be set right after.

In case you have your own distribution time, you can define it by clicking Base Data - Distribution - Time.