Deductions & credits

I have one client all week, but one day a week I have 2.  So, when I go from my regular client (client #1) to my one day a week client (client #2), I think that is deductible.  But, do I have to go immediately to the 2nd client, or can I stop for lunch if it is on the way and then go to the second client and deduct those miles from Client #1 to Client #2?  What is the time frame to get to the other client?