This is a chart that I made a while back showing the amount of time that a certain beat division lasts(which I call absolute duration) in a variety of tempos. I use it mainly to figure out how much time I’m working with when I compose, or try to determine the length of a tune while I put together a set-list.

• I color-coded tempos that are “tempo octaves” of each other.  This essentially means that they are tempos at a 2:1 ratio.  These tempos share the same absolute durations, but assigned to different beat values.
• To find the absolute duration of any triplet value, they should find the value for the same beat division, but in a tempo 150% the speed of the original tempo.  For quintuplets, one should find the same beat division, but for 125%(5/4) the original tempo.
• To find the absolute duration of multiple measures, multiply as necessary.  I tried to provide enough time values that it should usually only require multiplying by factors of 2 to get good approximations.
• In regards to quick calculation, I often generalize in the following ways:

1. There are slow tunes, medium tunes, and fast tunes.  For slow tunes(hovering around 60bpm), a measure of common time is about 4 seconds, so an 8-bar section would be 32 seconds, a 16 bar section is roughly a minute long, 24 bars is roughly a minute and a half.
2. For medium tunes, a measure of common time is about 2 seconds, slightly over/under for slower/faster medium tunes(medium is a rather broad term).  So a 16 bar section would be about 32 seconds.  This can be closer to 40 seconds for a slower medium tune, or closer to 25 seconds for a faster medium tune.  24 bars would be 48 seconds +/- a few.
3. Fast tunes hover around 1.5 seconds per measure of common time!  For disgustingly fast be-bop on amphetamines tempos, it can even go lower.  When this is the case, 16 bars of music amounts to 24 seconds, with faster tunes being closer to 20 seconds.
4. The longer the length of time, the more it’s worth it just to do the calculation to be sure(you all have smart phones anyways).  A musician’s estimate of the length of a tune can be horribly off.  Perception of time during performance is unreliable.
5. If estimating lengths for a set-list, factor in the inherent tendency to play things fast during live settings.