String to time (hh:mm:ss) using formula feature in CCPulse templates

Hi 

I have created a formula in the template wizard by adding up a few campaign handle times to calculate the Total Campaign handle time. 

So eg : I have : 
Campaign 1 handle time
Campaign 2 handle time
Campaign 3 handle time
Total Campaign handle time =  Campaign 1 handle time +Campaign 2 handle time+Campaign 3 handle time

The campaign 1,2 and 3 handle time are in hh:mm:ss format , however the formula that I created in the template wizard is coming up in string.

So the total comes up as 90 , instead of 00:01:30

Can anyone tell me if I can change the format from string to hh:mm:ss for formula in the ccpulse templates. 

Thanks