Generally, the staffing has to match the call volume/time change, especially at the peak hours. That is the reason why a lot of BPO companies arrange agents/callers online by every hour.
In your case, you required to have 50 agents/callers on the phones every hour regardless of the call volume/measure the key issue here is shift timings. You can plan Full time 55 agents/callers work from 7am to 4pm (1 Hour break, which includes Refreshment, Hygiene). For the remaining
4Hours, you can plan Full time 60 agents/callers work from 3:30pm to 8:30pm (1 Hour break, which includes Refreshment, Hygiene).
1. Fulltime Agents 55 – 9 Hours Shift (which includes 1 hour beak for refreshment and hygiene )
2. Part-time Agents 60 – 5 Hours Shift (which includes 1/2 hour beak for refreshment and hygiene )
You can also have 2 shifts! | Each 7 hours Shift! = you need 100 people every day.
Given the sick leave, training, vacation, I will suggest you need to have 55 + 60 + 5 buffer = 120 people to in pool.
This is a general plan for your situation. You may also contact me.
Hope this will/could help you in staffing.