How long would httpd service be down when recompiling is done via EasyApache ?

Under normal circumstances, the process involving recompilation of Apache and PHP would take around 15-30 mins. However the httpd service would not stay down for this long.

In a usual scenario if things are going well, it would be down for less than a minute.

This is due to the fact EasyApache does a dry run of everything first
to make sure it will work. This means Apache and PHP remain operational during EasyApache’s compile process.

Only when your configuration compiles and runs successfully does EasyApache replace your existing Apache and PHP installations, and during this short frame, the httpd service goes down and comes up.