formating dates and calculating length of time

[SorenN]

I am trying to figure figure out how the length of time between two dates (an online and offline date).
First the facts: Windows7 & Excel2010, I have tried formatting the cells to 'Date' which does not help and I have 1000+ date ranges to calculate.
The formula I found to do this is =DAYS360(Start_date,End_Date), which gives me a number of days such as 1140. My problem is that my source dates are 8-13-10 not 8/13/10 and pulled from a cell containing text and the date.
Here is a copy of my data, formulas and results:
[TABLE="class: grid, width: 500"]
<tbody>[TR]
[TD]E4(source data)[/TD]
[TD]G4(source data)[/TD]
[TD]I4(formula)[/TD]
[TD]I4(display)[/TD]
[TD]J4(formula)[/TD]
[TD]J4(display)[/TD]
[TD]K4(Formula)[/TD]
[TD]K4(Display)[/TD]
[/TR]
[TR]
[TD]Inst. 02-04-13[/TD]
[TD]Off 01-22-14[/TD]
[TD]=MID(E4,6,9)[/TD]
[TD][TABLE="width: 76"]
<tbody>[TR]
[TD] 02-04-13[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD]=IF(G4>0,MID(G4,4,9),"02-24-14")[/TD]
[TD][TABLE="width: 77"]
<tbody>[TR]
[TD] 06-30-13[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD]=DAYS360(I4,J4)[/TD]
[TD][TABLE="width: 64"]
<tbody>[TR]
[TD="width: 64, align: center"]#VALUE![/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[/TR]
</tbody>[/TABLE]

What options do I have to calculate the date ranges? Do I need to change all "-" to "/" and if so can you give me a tip on how to do that en-mass?
Thanks you all so much for taking a stab at this! I have learned a lot already working on this project and look forward to learning more with your help!
-Soren

 

[mfexcel]

if you need to calculate the difference between two dates: a simple formula I4-J4 would do.
since the date is actually stored as text in your case, you may need:
=value(I4)-value(J4)

 

[SorenN]

Thanks a lot mfexcel! The results on my sample data are close to using =DAYS360 when dates are 02/15/09. They are close enough that I am not going to worry about it and calculate the results!