Caldwell's choice to call a timeout with :36 seconds left and the Jags facing 2nd and 2 on Indy's 31 after the Jags came out running to just take the game to overtime has gotten intense scrutiny as any coaching choice that strays from conventional wisdom does. It wasn't so much the attempt to get back the ball that puzzled me. It was giving the Jags a shot to win it in regulation based on the idea Indy's D would be able to stop them from gaining 2 yards in 2 tries. If the Jags faced long yardage to-go or were more backed up towards their own end the choice would seem to back more sense.
The win probability calculator on AdvancedNFLStats.com can help get a feel for where the timeout moves from questionable to clearly the right move. None of these numbers account for the the particular teams. So subjectively tilt the odds as you feel appropriate to account for the relative strengths of the units involved.
Tied, with the ball on their own 31 and 36 seconds remaining, facing 2nd and 2, the Jags win probability was 57%. They had a 75% chance to pick up the short 1st down conversion. They had a 26% chance of scoring, but the Colts did have a very good chance to score if they got the ball back, leaving the Jags only 7% above the coinflip of overtime.
If the Jags "give-up draw" had been stopped at the line making the situation 2nd and 10 from the 23 the odds come out even to 50% win probability. A 21% chance the Jags score, but a 48% chance they don't get the 1st down, giving the Colts the ball with time still on the clock.
Examining other possible situations, it's less the yardage to-go making the difference between 2nd and 2 against 2nd and 10 than the field position. If the Jags had started from the 10 rather than the 23 then 2nd and 2 leaves them with a %50 win probability and if they had taken the kickoff out to the 35, 2nd and 10 is better positioning than the real life 2nd and 2 on the 31.
Whether the timeout was the right call in the given circumstance depends on your assessment of the teams involved, but with a bit better play on the Jags give-up draw or having started them a bit more backed up from the kickoff, the odds shift much more clearly towards Indy's favor.