Not knowing the chemical kinetics of the reaction, this is hard to answer. What I would do is this:(posted 8759 days ago)Collect all the data you can get (from the forum members, from data sheets, etc.). If you have one, use a spreadsheet program to evaluate them as described below.
Assume you got 6 mins at 1+4, 9 at 1+7, and 12 at 1+12, all of them at 200C, one-minute agitation, and for the same film to keep things simple. Now select a reference dilution, such as 1+7. Express all of the values as multiples of the time at reference dilution, i.e. 0,67 @ 1+4, 1 at 1+7, 1,33 at 1+12.
Draw a plot of these normalised times over dilution, and see if there is a correlation. If it is poor, this may be because the data you have were not all for the same values of the other parameters (film, agiation, temp). Then apply the procedure to a limited pool of data, such as "only those for film XYZ" or "only those for one-minute agiation", or, if nothing else helps, and if there are enough data, only to "those for film XYZ, at 200C, with one-minute agiation". Provided there is a correlation, try to extrapolate it to the dilution you are interested in.