Q:

In Excel 2010, how can I subtract two times when I also have the date in the cell and get the value in seconds?

I have a column of data as follows: 
 09/22/2015 10:25:22
 09/22/2015 10:27:00

I want to subtract 09/22/2015 10:27:00 from 09/22/2015 10:25:22 to get the value of 98 seconds. 
I tried formatting the cells to the form mm/dd/yyyy hh:mm:ss and then subtracting them, but it didn't work. 
Can I get the differences without removing the date and creating a separate column containing data in the format hh:mm:ss ?

A:

The result of subtracting one date from another, as with all date arithmetic in Excel, is a number wherein each "1" is one day. 
There are 86,400 seconds in a day, so the difference in your case would be 98/86400. If you format it as a number that's what you'll get. If you multiply that number by 86,400 you'll have the difference in seconds. (You may have to format it as a "number" for it to display properly.)  If instead of multiplying by 86,400 you format it as a time, you will get the difference displayed in time format (hh:mm:ss), which could be useful if you expect large differences. 
Now... when I tried your exact example on my machine the result of the calculation is an error message, "#VALUE!" Excel seems not to be recognizing them as date-and-times in that form, probably because that form is ambiguous for day numbers 12 and below. It seems to be storing it as a simple string. But if I type the date part as yyyy-mm-dd it works fine. dd-Month-yyyy (as in 23-Sep-2015) also works. So does "Jan 4, 2015". 
On the other hand, another answer says that the date format you used does work for them. These differences are likely a result of date format settings (localization settings) on the machines in question. You may have to compromise a bit on your date entry format, or write a formula that interprets the date-as-string and turns it into a date Excel can use. 
Try this: Assuming your date1 and date2 are in columns A and B... create column C with the formula =datevalue(A1) and column D with =datevalue(B1) . Then your subtraction (in column E) subtracts C1 from D1.  
In any case, removing the date part is not necessary. 

A:

Please use [ss] custom format for the resulting cell
If your source cells with have General format (i.e Text, not DateTime) , then please use =TIMEVALUE(RIGHT(A2,8))-TIMEVALUE(RIGHT(A1,8))
instead of =A2-A1

