I see no point in taking home test with the first urin of the day if you are going to dilute for the test anyway, to me it's a complete waste of a test considering the only way you can pass that one is if the THC is below 50ng in your body. The better idea would to dilute then take the hometest considering that's how you will take the real test.
That would be a better idea - if the human body was some kind of electronic machine operating on fixed settings. But the human body is not this (and thank god for that - its good to be a human being!). THCA concentrations, fluid volume, and urination sessions fluctuate daily. Just because a person had diluted and passed a U/A on Tuesday 4pm does not necessarily mean that the person will dilute and pass on Wednesday 5pm.

By using the first void, you are testing yourself when THCA concentrations would be at their highest and had not been affected by any fluid consumption prior (aka the "worst-case scenario"). And if the home tests consistently show a negative under that "worst-case scenario" (regardless of line intensity), youre good to go.