I always use a timer. Sense of time can change when meditating and there have been times that when my timer wasn't set or malfunctioned I accidentally meditated longer than I meant to, which can be an unsettling experience, and create distracting fears in future sessions.
Wow! That sounds intense, I don’t think I’ve ever meditated for longer than 30 minutes. Do you always meditate till your timer go off, or do you use it as a kind of maximum timer?
yes, I always meditate until the timer goes off - once you set the timer you don't think about the clock or time anymore, and you trust the timer with that task so your mind can ignore it. :-)
I usually meditated 1 - 2 hours / day back then. Longest session was over 3 hours. I preferred sessions that were 1 hour because it seemed like 45 minutes was a minimum for getting to a decent level of concentration for me, and so I could sometimes enter a pleasurable flow state and things would be "happening" at that point.
I usually use a timer, but there are periods of time when I don't want the jarringness of a sound to end it. Then I'll use a mala, moving one bead for each breath. You can use it with your timer a few times, and get an approximate idea of how many cycles your standard meditation length is. If you use two of the short bracelet style or a Jodo Shu style juzu, then each time around the first string is one bead on the second string. You can set your time by where you hold the second string at the start of your session - hold it so that you will count the correct number of beads before reaching the guru bead.
For really long sessions or when counting short mantras, use the hanging beads to count times round the second string.