Time::Format_XS is a companion module for Time::Format, to speed up time formatting.
Install this module, but do not use it.
The Time::Format module (q.v.) is a handy and easy-to-use way of formatting dates and times. It's not particularly slow, but it's not particularly speedy, either.
This module, Time::Format_XS, provides a huge performance improvement for the main formatting function in Time::Format. This is the time_format function, usually accessed via the %time hash. On my test system, this function was 18 times faster with the Time::Format_XS module installed.
To use this module, all you have to do is install it. Versions 0.10 and later of Time::Format will automatically detect if your system has a compatible version of Time::Format_XS installed and will use it without your having to change any code of yours that uses Time::Format.
Time::Format_XS is distributed as a separate module because not everybody can use XS. Not everyone has a C compiler. Also, installations with a statically-linked perl may not want to recompile their perl binary just for this module. Rather than render Time::Format useless for these people, the XS portion was put into a separate module.
Programs that you write do not need to know whether Time::Format_XS is installed or not. They should just "use Time::Format" and let Time::Format worry about whether or not it can use XS. If the Time::Format_XS is present, Time::Format will be faster. If not, it won't. Either way, it will still work, and your code will not have to change.