Limiting number of same entries in a column

Hi all

Please see attached agent schedule.

I want to limit the number of agents choosing their lunch start as "12:00" to 5 agents, "12:30" to 6 agents, "13:00" to 6 agents and so on...

is there a way to achieve this where if the 7th agent chooses his/her luch hour say "13:00" o'clock they get a message asking them to choose another time?

Many thanks

Johny

Hi Leith

Here is the schedule I want to implement.

11:30 2 agents
12:00 5 agents
12:30 6 agents
13:00 6 agents
13:30 6 agents
14:00 3 agents

Minimum lunch hour 30 min, max lunch hour 1 hour 30 min.

Many thanks