Consider the following example. First create an empty column where you are going to place your calculated event LENGTHs. For example, if the PLACE (event start) and CEXIT (event end) entries are in columns A and B, then create a new column C (highlight area, and then select Insert/column):
A B C
place cexit length
1 55 11
2 78 34
3 45 1
4 64 22
Then enter as the first entry (C1) in the length column: =IF(b1=1,99,a1-b1+1); hence if CEXIT=1, it selects the LENGTH to be 99, else the LENGTH is PLACE-CEXIT+1. Then copy this entry and paste into the rest of the cells in that column.