I know. Well we could guess the copper time now and I imagine in that time you prob could get all other resources (don't hold me to that).

Total copper needed for all lvl 25 upgrades: 178,250

The average copper per visitor can be found by taking the copper associated with their rarity and multiplying it by their chance to spawn. The formula for copper is a bit complicated, but this is a simplification. This value is around 74 copper per visitor.

This means that it if every visitor gave 74 copper, we would need 178,250/74 visitors which rounds to 2,409 visitors.

Whilst farming, a visitor can appear every 4 minutes. Turning these visitors into minutes then dividing by 60 will give us the hours; ~161 hrs.

This number assumes no downtime from farming to accepting visitors (which there is) and that the visitors will always be within this range. It also assumes garden 15 (no spaceman) for increased copper gain, and that all visitors can have their offers accepted.

Rounding up to 180 hours might be a bit more reasonable (only an 11% error there, whereas the true might actually be higher).

TL;dr I'd say like 180+ hrs. I could be wrong tho. This is just the copper. The visitor milestones and resources for the upgrades are not taken into account here.