The expected value in terms of artifact wealth is the same (within rounding error) for all digs.
1d 8h +/- for a 3% Epic/97% Poor chance.
If you assign value 1 to poor artifact, then common is worth 5, uncommon 25, rare 125, epic 625.
Default time for 100% common artifact (value 5) is 8 hours, so you get 5/8=0,625 per hour.
Expected value of your example is 3%*625+97%*1=19,72
19,72/32 hours = 0,616 per hour, very close to 0,625 per hour.
This means that it does not matter which dig you choose, on average you will gain the same value per hour. Difference is that with more digs (shorter) you have more frequent chances to get the artifact you want.
Edited 9/19/2024 12:47:42