Geek Time for iPhone is a native implementation of the hit time-telling website GeekTime.org
The following information is taken from the Geek Time website:
What is Geek Time?
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There are 86,400 seconds in a day. The closest power of two is 65,536. Instead of using seconds, Geek Time divides the day into 65,536 units and then displays those units, relative to coordinated universal time (UTC), in hexadecimal.
The day is just the 0-indexed day of the year in hexadecimal (at UTC).
The glyph underneath is (assuming your browser supports it) an example of the Unicode character at the code point corresponding to the current Geek Time.