GPS Precision without correction

I\’m new to this, thanks for your patience.
It\’s my understanding that correction affects accuracy, but not necessarily precision. If that\’s correct, how fast does precision drift over time. For example, I want to create a topo map of a small field (15 acres), absolute values aren\’t necessary, I only care about the relative topography. Is there a time window in which I can expect uncorrect gps readings to have precision in the sub 3cm range? If so, is that window measured in minutes, hours, days? I have the simpleRTK2B – Basic Starter Kit.