What seems a bit odd is that it looks like the 3 minute @ 20C strip is lighter than the 2 minute strip at 20C. Did you label them correctly? If so, then there's a change you've got another source of variation there.
BTW just checked my chemistry and it develops a fully exposed (lights on) strip in about the same time as yours to full black; I timed 26 seconds. This is at approx 17C.
BTW just checked my chemistry and it develops a fully exposed (lights on) strip in about the same time as yours to full black; I timed 26 seconds. This is at approx 17C.
