This hint is perhaps obvious, but I didn't see it anywhere and it can be useful to know. If you click on the Spotlight menu bar icon, it will tell you what it estimates the remaining time to create the index will be (i.e., "About 5 hours remaining"). If you hover your mouse over the Spotlight menu bar icon, however, it will tell you a percentage completion figure instead ("Indexing volumes. (6% done)"). A percentage can be nice because OS X's estimate isn't always that good.

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