So typically, the career looks something like this for a SWO (surface warfare officer); two, two year division officer tours (on a ship), a two year shore tour, back to a ship for another two years as a department head, then another shore tour for several years, then eventually back to a ship for XO (2 years), then eventually CO (2 years) So maybe around 8 years total on a ship.
Also keep in mind naval ships go through a two year work up schedule to deploy, so much of that "ship time" is not underway. Maybe 1/3 to 1/2. Also, the only actual bridge watch standing time is done on the first and second division officer tours. Department heads don't stand bridge watch.
Further diluting the experience is the fact that those two divo tours are competing with 10 other junior officers plus second tours to get bridge time. Schedules also mean some divos hardly get underway, or never deploy, with maybe only a few weeks underway before moving on to their second tour. Some second tour division officer don't stand much bridge watch as well.
You can see, it is fairly easy to lack much tangible experience. Now they do make due with what they have, and train hard in the short time period, but it is no substitute for experience.
Remember the OODs on those grey hulls have maybe several months of underway experience at most, and a shiney pin on their chest.
Now as for actually standing OOD qualified and on your own, I'm afraid you will find that answer quite scary. Just doing some basic math, best case MAYBE 480 hours conservatively (but it could be far less). If anyone wants to debate that, I can bring up the math.