Strand Test w/ Filler instructions?

I have been coloring for about 5 years, but either stayed the same or went lighter....final color was platinum=no pigment. Now that I want to go darker, I want to do a strand test. I want to eventually get back to my natural color of med/dark blonde. I want to go a shade or two darker every 4 weeks so it's not such a drastic change. I used filler the first time I tried a tad darker shade and it worked great! My questions are:

1. When doing a strand test, I should use the filler on the section of hair, right?

2. Do y'all cut a section of hair off or leave it attached? I understand you can do both.

3. Do you use the same box of color? What I mean is, do you do the strand test, time it and then proceed to use the same mixture? Does sitting for that amount of time 'mess' with the unused (as of yet) haircolor?

Thanks!

Edited by KellyH

Thanks! It's called 'Lock-In Blonde'. It went on a gold/orange, so I'm assuming, yes. I went from a Platinum to Light Ash Blonde using it. It worked great.......completely even color. I'm going to try a darker light ash blonde next. Baby steps......:D