The situation I'm picturing where it could take a few years is if the bike lanes are raised up to the same level as the sidewalk. Which can take a long time because it means moving existing curbs, which means moving catchbasins (curbs direct water flow) and often light posts (should be near edge of road for accessibility purposes - maintaining clear walking path, having push buttons and audible signals at edge of street). Doing either or both of these things means stuff is getting moved around underground, and underground is a very busy place (sewer, water, natural gas, buried electrical, signal infrastructure, old foundations, ... And all these are at different depths, with different separation requirements, severally limiting what can go where). And add in a busy location like Market Street, and maintaining access all the time, and probably limiting working hours to minimize impact on residents/businesses. The time would add up fast.

There's no upper limit to how long you can take to do something.

Lower limits, sure, but no upper ones.