Recently my torah-study group was discussing the events of Parshat Sh'mot, and someone claimed that people could only gather straw for bricks in the fall (I don't know if that's true) and the exodus was in the spring, so "obviously something was wrong in the timeline here". I countered that the text doesn't tell us how long it was from Moshe's initial "let my people go", through all the plagues, to the exodus, but we didn't find any commentary on this in the assortment of chumashim we had to hand. It came to light that some of us assumed this played out over a few weeks while others assumed it took months.
We know some small lower limits (like the plague of darkness lasted three days), but do we have sources that speak to this question? How long did the harsher service and the plague show-down last?