You can do it with adding macros in /librenms/config.php
For example
Macros Time periods
$config[‘alert’][‘macros’][‘rule’][‘From_15_to_17’] = ‘HOUR(NOW()) BETWEEN 15 AND 16’;
$config[‘alert’][‘macros’][‘rule’][‘From_8_to_17’] = ‘HOUR(NOW()) BETWEEN 8 AND 16’;
$config[‘alert’][‘macros’][‘rule’][‘Mon_to_Fri’] = ‘DAYOFWEEK(NOW()) BETWEEN 2 AND 6’;
then you just add that macro in your alert rule