Well how does the floor look now?
Do you have any stains?
Sealer applied correctly and maintained using ph neutral cleaners can last a long time.
Here is the list of performances for a impregnating sealer.
1)To temporarily inhibit the intrusion of staining agents into the surface of the stone.
End of list.
After 2 years if you notice wear or other issues on the surface of your stone it may be time for maintenance.
We maintain our rugs, carpets , lawns, auto, wood floors,
dry cleaning-heck even the dog goes to the groomer.
The marble seems to get neglected!!