determining time step size in transient analysis
 

i would like to perform a melting phenomena that takes hours using transient analysis in fluent. i am confused by what i must set as the time step size and no of steps. to define , i need to solve so that i get a result every 10 mins and that must go on for 3 hours. i find that its all in seconds and am not sure about how the cfl no may be affected.
i am very much new to this area. in fact i am only in my sophomore year in engineering.
please explain me!
thanks a lot!!