For Y-DNA, a Most Recent Common Ancestor is defined as the closest direct paternal ancestor that two males have in common (such as a grandfather or g-g-g-grandfather).
In general, the closer the match in haplotypes between two individuals, the shorter the time back to a most recent common ancestor.
For instance, if two individuals share 35 out of 36 markers, they almost certainly share a more recent common ancestor than two individuals who share 32 out of 36 markers.
Calculating the Time to Most Recent Common Ancestor is based on probability and is not an exact science. We can identify the most likely time that a common ancestor might have lived, but there will always be a degree of uncertainly. For this reason, it is better to think of TMRCA as a range of time rather than a point in time.
When searching the Sorenson Database, SMGF provides a TMRCA page (accessed by the icon) for each participant shown on the Results page. The TMRCA page contains additional information for interpreting Time to Most Recent Common Ancestor.