substract two time logs based on a string

I am trying to calculate the amount of time elapsed between two logged events. Column D has the person's ID and column O has the elapsed time. The raw data has multiple ID's but everything is in time numerical order.

I am trying to get Excel to subtract two time stamps in column O based on the ID in column D. My formula is =SUM(O102-O101). This is assuming that line 101 and 102 is the same ID. It could be o154-o101. I have tried several ways of embedding this in if functions but can't seem to get it to recognize the string correctly or perform the sum function.

So you want to subtract the time associated with the first occurence of the ID from the time associated with the second?

Will there only be 2 occurences of the ID? If so try

=SUMIF(D101:D200,A1,O101:O200)-VLOOKUP(A1,D101:O200,12,0)*2

where your data is in rows 101 to 200 and A1 contains the ID of interest

Here is a sample. I think it will help you to settle your problem.

Thanks, Daddylonglegs. I will give this a try.

Thangs SGLife. This is very helpful.