Calculation based on multiple conditions

Im looking to perform subtraction of time in multiple columns. I'm thinking this may be a IF logic.

What I'm trying to calculate is how long a person waits in a room by themselves until the next person comes to see them.

Starting with column N and going right. row 2-4 is where I'll be looking. Calculating the wait time is the goal. I want excel to look at various options to calculate this.

For example in row 2, Starting at O, provider left at 818 and the MA came in at 819. the wait time of 1 min would populate P. MA leaves at 8:22 and then next person doesn't come in till column AE at 8:24. the next wait time column I want it to populate is Column AB and leave the W and S wait time columns blank.

But..for example in row 4 this is a different scenario. More times are entered so excel will calculate the wait time to populate S, W and AB, but leave P blank.

Thanks for your help.