A website gets visitors 24 hours a day, 365 days a year. A website can sell round the clock. Good website hosting services provide various levels of site uptimes but is most cases it should be over 95% of the time.
However, you cannot leave it to the hosting service providers to monitor how long your sites are up & running .
There are several tools to monitor & alert you of cases where your website is taken offline . This could happen due to several reasons.
Wordpress has released the module for 