You can file for an abatement when the actual tax bill goes out. That bill is received on January 1, and the abatement needs to be filed between January 1 and January 31. The assessors will review the property.
They will either abate the value for an error in listing, adjust the grade, correct the area, etc. or they may deny the request for the abatement if they find that the original value was correct. If the taxpayer still disagrees, they can take their case to the Appellate Tax Board and present their case before a commissioner and that Board will make a decision on the value.