1. You will probably want to use the "Timer" method, or the "time" method (shown used in MyTime() below) to keep track of that. Have a set of SendRequest#() subs that use the first functions, and another set that use the other. Switch between the two after you notice that 10 minutes have passed, set the duration of the test to 20 minutes.
strhour = hour(time)
strminute = minute(time)
strsecond = second(time)
strMyTime = CStr(strhour & ":" & strminute & ":" & strsecond)
2. If you want to read a text file, and use that to replace form data, then you proabably want to use the FSO methods to open a file and replace strings in the form data with the values you get from each line. That works pretty well for me.