Index match sumif for a running total

Hi, im trying to make a floor plan for my rota.

I have put the whole day in 15 minute intervals and Im looking to get a rolling count of how many people are in at each interval (example in column L)

each member of staff works 8.5 hrs so a 9 am shift would finish at 17:30 (shown in A16 - b21)

Im looking to have it so when I drag the formula down in works out how many people I have in at each 15 min interval (as shown in the example ) and when I drag across it goes to the next date.

I hope that makes sense if not please ask.

Many Thanks

Luke

Just in a number format, I have highlighted in yellow

the table in A1:g14 stays like it is, its the table to the right that I need to work off the table A1G14.

Cell A1 – H14 is the team rota, the time in each cell is the time they start their shift i.e. B8 Staff 6 starts at 12:30
Cells B16 C21 is the start time and the end time of the shift i.e. if staff 6 starts at 12:30 they finish at 21:00.

In Columns K – S I need this time frame to be counted within each 15 minute interval.

So in the example in Column M two members of staff start at 9:30 (Staff 1 & Staff7) so in column M from 9:30 till 12:30 it counts as 2 members of staff in, but at 12:30 when staff 6 & Staff 12 arrive the number increases to in column M row 26 to 4 members in. This continues to increase as more staff arrives throughout the day, until the staff members shifts come to an end, so when the 9:30 starters (Staff 1 & Staff7) leave at 18:00 the count drops to 4 members in.

Im looking for this to be automated so it can count the staffing levels for each day, so in column N it would reference the shift times in C3 : C14.

I hope that makes more sense, I apologies that the break down was so bad, I was in my own head on this one.