Multiple specific gravity samples for a hydrometer can use up a fair percentage of the volume of a one gallon brew. If I were doing one gallon batches I would use time as a safety factor for not bottling before the fermentation was complete.
The sanitizer in both sides of an S-style air lock is at the same level. This means CO2 is no longer being produced by active yeast. The level will also be affected by changes in air pressure but air pressure usually does not remain static over a period of days.
The beer begins to clear. When CO2 is no longer being produced by active yeast the sediments suspended by CO2 and excess yeast will begin to drop out of solution.
Time, also known as patience can be key. When the beer clears without cold crashing take a hydrometer sample. If the SG is at, or safer yet, lower than the apparent attenuation given by the manufacturer your beer may be ready to bottle.
I normally allow three weeks for a moderate 5 gallon OG beer to be ready to bottle or dry hop. I do take a couple of SG readings to confirm this.
Take good notes for the next times you brew this same recipe.