Can i get jot form to auto calculate a time

ik would love to know if it is possible to let jotform calculate time:

for example i use jotform for freelance people to fill in their daily details  (http://form.jotform.com/form/13562238261)

now i would like to know if i can get jotform to do the following:

(sorry I am dutch)

eindtijd (time someone end working)   minus  begintijd (time someone starts working) =  value (time)

please let me know if this can be handled in jotform..

Ivo