Based on surviving recipes (which are generally vague and hard to come by in earlier periods, so I'll mostly be referencing 15th and 16th century sources), they may have some type of vague indication on what type of heat to use and how long to bake something, but certainly not precise measurements, and things like temperatures (and therefore bake times, since the two are pretty strongly connected) were probably learned through practice and experience. Temperatures could have been accounted for in a few ways. Many of the oldest recipe books we have, such as the Forme of Cury from the kitchens of Richard II, are from the households of people of considerable wealth, who would have generally had multiple ovens, each of which could be kept at different temperatures, if necessary, or larger ovens where a temperature differential could be made fairly easily by focusing the fuel to one area.

​

A few examples: the 1553 Das Kochbuch der Sabina Welserin (Armstrong trans.) has a recipe for Spanish Pastries (essentially an almond/sugar/butter paste rolled in a "firm dough with eggs and fat"), the baking instructions for which are "...let it bake in a weak heat, with a hot cover over the top." Weak heat gives sort of a relative temperature to work with, and if we think about that in terms of modern baking temperatures, by looking at the recipe and applying what they know about baking, experienced bakers would probably figure a weak oven to be maybe somewhere around 350F or 175C, which is the recommendation from modern transcriptions. It also has a quince bread (less a bread, more a paste spread onto wafers) recipe which instructs "... lay them on a board and lay it on the oven. Be careful that the oven is not too hot. And when it begins to dry out on top, then put them on a board in back of the oven, until they have dried out." This one also hints at a temperature differential within an oven, given that it instructs to move the bread, and while "not too hot" doesn't seem much different from "weak" in terms of temperature, the recipe is as much about drying them out as heating them up, so the modern suggestion is around 300F/150C.

Two Fifteenth-Century Cookery-Books from mid-15th century England has a quince pie (which is actually a pie) recipe, the cooking instructions for which are to "... late hem bake ynog [let them bake enough]." Not extremely useful if you're trying to set an oven temperature and timer directly from the recipe, but if you're baking under the eye of someone who has been doing it for decades, they would probably have the knowledge to make an educated guess based on their experience with baking pies.