I also realised that i need to take into account if the nail is pure iron or impure iron. Im pretty sure that the nails would be impure so they would rust more quicker than pure iron nails.

i found out about ferroxyl indicator solution wich contains potassium ferricyanide and phenolphthalein and this turns blue when it detected metal oxidation. so if i can get some (i hear there are is a gel that contains potassium ferricyanide) i could add some in the solution and compare each one.

Also i forgot to mention my hypothesis for the vinegar. the vinegar increases the conductivity of the water and is also acidic so i can assume this will speed up the rusting.