Having trouble converting milliseconds to a nicely formatted hours, minutes, and seconds string

Question

I’m using Rails 4.2.3. I want to take a time in milliseconds (a duration, not a UTC time) and convert it into hours, minutes and seconds. I’m trying this

    Time.at(time_in_ms).utc.strftime("%H:%M:%S") 

but this doesn’t seem to be working. For instance, in my POstGresql database, I have this amount of milliseconds

3601000

and the above is producing

16:16:40

even though it should produce something like “1:00:01” (one hour and one second). What is the proper way to convert time in milliseconds to a nicely formatted hours, minutes, and seconds?

Answer 1

Time.at() expects a time in seconds after a certain epoch - 1 Jan 1970 00:00:00 UTC - so your code needs to divide the ms figure by 1000 first:

Time.at(time_in_ms/1000).utc.strftime("%H:%M:%S") 

EDIT: I just rechecked the Ruby docs: the below rider is incorrect! The passed-in number of seconds is assumed to be in UTC, so at() does the calculation THEN factors in the UTC offset. The above .utc undoes that factoring, and is required.

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Of course, the problem with that code then becomes your current time zone. Say you're at UTC-5 (New York time): Time.at(3601000/1000) becomes "01:00:01" local time. Converting it to UTC would subtract five hours from the hour figure, making it "20:00:01". So remove your .utc conversion too:

Time.at(time_in_ms/1000).strftime("%H:%M:%S")