Select the crop from the drop down box, enter the percentage number showing ready on the crop without the percent (%) sign, select the hour of day and the day for where you are.
The timers on Farm Town seem to be just a little erratic so there will be + or - a few minutes on the timing, the seconds displayed are static and there now just to keep the script engine happy. This will give you a time close enough to schedule a harvest party.
The results are real time days converted from Farm Town days.
The time function seems to be working fine and the time to harvest and the waste time seems correct. The actual day for harvest may or may not be correct so double check the grow time left to be sure. Don't depend on the crop waste Day and time, it should be accurate but it is the drop dead waste time and does not allow for the time to harvest.
Check your crops as you usually do and don't depend on this for an accurate time for harvest. If you notice any time or day issues please let me know, it would help to know what crop, percentage, hour, day, and location so I can see what went wrong.