How soon after dosing do I test my water?

[matpat]

I just began dosing today with KNO3, KCL, Fleets, and Flourish Iron. The tank has been "growing" for nearly six weeks now (2 weeks with current substrate). I have tested only the pH, GH, and KH since planting. Here are the water parameters (all have remained stable since day one)...

pH 6.8-7.0
KH 7
GH 5

Since dosing earlier today after receiving more test kits...
pH 7.2
KH 8
GH 6
fe .1
PO4 .01
NH3/NH4 0
NO2 - 0
NO3 - 1
(Fe, PO4, NH3, NH4, NO2, NO3, were all 0 yesterday)

I'm using Chuck's Planted Aquarium Calculator to figure dosing...except for the fleets. I dosed close to 5 hours ago and my NO3 and PO4 do not seem to be quite right. Should I wait until tomorrow and retest or is it possible that the plants have actually used up what I put in?

Any help would be appreciated. Thanks.

[SCMurphy]

It depends on what you want to learn from your test. Do you want to know the levels that your dose creates? Wait until the tank is turned over twice by the filters based on their capacity.

Did you want to give the plants a chance to use some before you test, wait a day.

Do both and subtract to get a rough estimate of nutrient usage. Do this a few times and you will be conducting an experiment worthy of a science fair.

[matpat]

Thanks for the input Sean. I was hoping to get the NO3 levels up to about 5ppm and the PO4 to 0.5ppm as a starting point. Seems like both are a bit low...but better than they were yesterday. I think I will try testing again tomorrow afternoon. If the results drop, should I dose again???