I don't know which one you are considering the slow Jeffco but they have three different cross linker speeds.  The standard is 1307 with 3102 hardner, next is 3103 as the medium speed and 3156 as the slow speed hardener.  They have 10-15, 20-25 and 30-35 minutes as their gel times (if left in a concentrated mass that really gets an exotherm going) but of course if you spread it out in a laminate quickly, it will be considerably longer open time.

 

Also there are many other systems that are considerably faster or slower.  Some of the stuff I've used on large laminates is in the hours of gel time.  Others won't really get going until you add heat so if you have a big project, don't limit yourself to the relatively crude single phase epoxies like WEST and Jeffco. Also for structurally more challenging applications, there are much higher performance two phase epoxies.

 

Dan

 

Dan