Roster calculation help needed!!!

Hi all,
I have followed the forum for some great formulas that have assisted me in tracking rostered hours using Excel.

My issue is this, I run a restaurant and not all shifts have specific end time so when we write the roster, some shifts are written as '3pm-cls' with the "cls" representing the closing of the venue. As a rule of thumb, I would like the "cls" to represent 11pm, in order to calculate the estimated hours work for that day on the roster. The reason I can't always write that a shift is intended to end at 11pm, is due to the fact that sometimes we close early and other times we stay late. Staff unfortunately take the posted hours very literally and expect to stay til or leave by 11pm, which is not always the case.

Can anyone help me with a formula that calculates hours, when written (e.g. 3pm-9pm) and can also deduct that a term like "cls" is intended to represent 11pm?

PLEASE help and THANK YOU in advance!!