That is not how it worked for most.
The vast majority of the population were farmers of some sort living in tiny villages. The market was open only rarely: perhaps every two weeks, but there is no reason to assume a regular schedule! Market days where what made sense for the village - no market when everyone is harvesting, or when the weather is bad. Everyone knew when that day was and he whole family went to market on together.
Markets were not "craftsmen" with their stalls. There were some traveling traders who worked like that. Often you just knew what you had at home to trade and were just making arrangements.
A set workday/shift is required for several jobs where one person cannot work unless someone else is working too. Assembly lines are an obvious example, which the British seem to have started development on first (though they didn't look anything like Henry Fords assembly line you can see the start of this "The Wealth of the Nations"). Shift work is also required when you all depend on a steam engine - miners can be paid by the ton and thus leave at any time, but as soon as the man running the pump leaves the mine floods and everyone else is forced to stop.
Two cabinet makers in a shop (this implies a large cities to need two cabinet makers in a shop as opposed to journeymen who travel between villages doing work) by contrast only rarely are doing something that needs two people (and often when they do they have an apprentice). They can each leave to go buy something whenever they feel like it. Most jobs would be this style, there is a deadline of when the job needs to be done (sometimes flexible sometimes not), but so long as it is done on time nobody cares when you do it.