depends on how much beer you want to waste pouring it out after the test.
personally, i studied a lot of BJCP stuff to figure out what i could comfortably FORGET, and I will again use my hydrometer if there is a problem I cannot figure out otherwise.
(I don't care about 4.3 versus 5.8 so I drink till i feel it, and don't enter competitions. ymmv. have fun!) one day won't kill you, unless you happen to die.