In any case, I think it's more than just the time payoff. Getting repetitive tasks automated allows you to reallocate that cognitive overhead to other details, and that's a payoff that's hard to quantify, but is critical for leaving your mind free to focus on more important complexity.
If for example it only took 15 minutes of manual work it's highly unlikely that the payback of automation would occur any time soon. That's especially true because the 2nd or 3rd time there may be different special cases and you'd have to go back and change your automation.
Automating a task usually means each important parameter is entered only once, that all steps are completed, and that the results are checked.
Spend 10 hours writing a script to automate 50x10 minute jobs. You spend an extra hour, but you end up with 50 consistent results, rather than 40 successful jobs and 10 with minor mistakes.