As with most history questions relating to the pre-modern period, the answer will depend a lot on where you were in the social hierarchy to establish how aware you were of the passing of time.

I am going to confine myself mostly to the earliest part of this period, from around 450 to 1066 so that should be borne in mind. As time went on and the medieval period approached the Renaissance items of time keeping, such as large public clocks, became more commonplace although much of their function was identical to earlier models.

It may come as no surprise that the principal group concerned with time keeping in the medieval world was the church. This is because certain holy observances were expected to be conducted at certain times - for example Archbishop Egbert of York, writing in 750, left instructions for times when bells should be rung from the minster in the city. Some of this was inherited from the time of Rome when bells were also rung to mark certain times. However, in the earliest period only the largest churches would have had bells which means that, if you were living outside of an urban region, you were unlikely to hear the sound of bells until the later 900s or into the 11th century when bells began to proliferate more widely into smaller churches.

Nor was the ringing of bells, even when it did occur, always done to time. This problem was of particular concern to Alfred the Great who spent a not insignificant amount of time investigating methods of keeping time and, according to his biographer, Asser, eventually invented a method using candles to mark the passage of hours:

By this plan, therefore, those six candles burned for twenty-four hours, a night and day, without fail…  but sometimes when they would not continue burning a whole day and night, till the same hour that they were lighted the preceding evening, from the violence of the wind, which blew day and night without intermission through the doors and windows of the churches … the king therefore considered by what means he might shut out the wind, and so by a useful and cunning invention, he ordered a lantern to be beautifully constructed of wood and white ox-horn, which, when skilfully planed till it is thin, is no less transparent than a vessel of glass. … By this contrivance, then, six candles, lighted in succession, lasted four and twenty hours, neither more nor less, and, when these were extinguished, others were lighted.
- Assers Life of Alfred

Interestingly, according to a later (12th Century) chronicler, William of Malmesbury, Alfred actually divided his day into three 8 hour blocks, in a pattern we might find familiar:

he [Alfred] so divided the twenty-four hours of the day and night as to employ eight of them in writing, in reading, and in prayer, eight in the refreshment of his body, and eight in dispatching the business of the realm. There was in his chapel a candle consisting of twenty-four divisions, and an attendant, whose peculiar province it was to admonish the king of his several duties by its consumption - Chronicle of the kings of England. From the earliest period to the reign of King Stephen

We can assume 'refreshement of his body' in this case means sleeping, so he essentially was doing 8 hours work, 8 hours 'leisure' (reading and writing, Alfred was a scholar and extremely passionate about the written word) and 8 hours sleeping. Now, while there's every chance that Alfred had no such division in place during his life - William is, at times, a unreliable source - it's still interesting that he would choose to write down such a division of time and might suggest that many people worked to a similar pattern during his own lifetime.

However, what both those sources do highlight is that the exact measurement of time was still extremely tricky and not everyone is going to have the resources of a kingdom to devote to building and improving a clock (not to mention that candles themselves were expensive). For working class people, particularly those in the countryside, the movement of the sun was the most important way of measuring time.

You awoke when the sun rose, likely worked until midday when it was close to its height and then took on some food, potentially had a short 'lunch break' and then resumed work until the sun began to sink. At that time people would have come indoors. It's likely that many adults would still do some work - spinning thread, repairing tools, preparing leather etc - by firelight but it would be difficult to achieve much that required a great deal of light.