A solid wood surface finished with a polyurethane based varnish requires no maintenance at all. Nevertheless, some scratches, cut marks and other similar damages might be difficult to repair with touch-ups; therefore extra care will be required.
On the other hand, a mineral oil finishing needs to be applied periodically but in turn, it allows you to easily fix minor damage, and to renew the surface whenever necessary.
Assuming you followed the instructions regarding finishing before installation, you will need to apply a new coat of oil every month during the first year and once every six months or so ever after. You should be advised, however, that there is not any carved in stone set of rules regarding how often you should re-oil your butcher block. A lot of external factors could come into play. Dry winter months, air conditioners, the vicinity of a stove burner, for instance, will cause the wood to dry up faster and, therefore, require a more frequent re-oiling. The golden rule, therefore, would be to apply a new coat of oil every time the wood begins loosing its “oily shine” and starts looking dry.
For maintenance purposes, you will need to oil the topside and the edges only. As the wood is already saturated, it might take a bit longer for the oil to completely cure and some excess oil might remain on the top surface.
Sanding the damaged area and re-oiling it can conveniently repair almost any scratch, cut mark, watermark, food stain, or similar damage. Similarly, if you choose to re-shape your solid wood top, you have to subsequently oil carefully all the exposed areas.
Routine cleaning is done with soap and water; do not use cleaning solutions on your butcher block under any circumstances. The butcher block should be cleaned after each use and at least once a couple of months when not used.
Please be advised that a mineral oil finishing will offer a weak protection against harsh chemicals such as bleach or pipe-draining acids. Polyurethane-based varnishes do not have these limitations.