Once again, rest for 60 seconds...
Next weekend twice each day would be best. If you need to stop completely for him to recover a bit and avoid orgasm, that's fine. Most men will tolerate just testicular stimulation during these pauses without reaching orgasm. About a five minute pause will usually do it. If you need to pause two or three times to get in the total amount of stimulation, don't worry. That's pretty normal, especially after the first few days. Just don't count the time during the testicle stim as part of the 20 minutes.