Clocks existed then though. The oldest clocktower in Europe that still exists was built over 100 years before Galileo was born, and time measurement existed longer than that. You can measure time fairly accurately with water clocks which had been known for thousands of years before Galileo. Not having "modern" pendulum clocks yet doesn't mean that they didn't have any way to measure time. Even without water clocks you can get decently reliable measurements of time with rhythmic chants (think how today we might say "one Mississippi, two Mississippi, etc.). Early alchemical recipes often include time measurements in chanting a specific prayer or passage a certain number of times during a specific step. Sure you're not going to get milisecond level accuracy this way but you don't really need that for a lot of things. Hero of Alexandria built mechanical automata 1500 years before Galileo using pulleys and weights as timers. Time measurement not only existed before pendulum clocks, it was pretty decent.