Expiry time for memcached cache of interwiki table.
The units are in seconds.
( 60 s e c / m i n u t e ) ∗ ( 60 m i n / h o u r ) ∗ ( 3 h o u r s ) = 10800 s e c o n d s {\displaystyle (60sec/minute)*(60min/hour)*(3hours)=10800seconds}
