time format when I take frame stills using VLC

[dd331]

I am trying to capture the trajectory of an object in a mov. file, so I have been taking stills from the .mov file as the time progresses. A typical .png file from the stills has the name
2011-10-08-23h59min01s24. Clearly this correspond to the year-month-date-hour-minute-seconds, but how about the last number 24? Anyone has any idea what this is. This doesn't seem to be the frame number, because this number goes up and down as the time progresses. Any help would be appreciated.

In any case, I would like to be able to know the time of the stills to better than a second. Is this even possible using VLC?