Do action once but only repeat it after x time - php

Question

So basically, i need to notify a user if:
a) sensor disconnects and there hasn't been an alarm sent in last $send_threshold
b) if alarm sent on same day and greater than $repeat_threshold.
Example values of the variables
$send_threshold = 12 * 60; // 12 min
$repeat_threshold = 2 * 60 * 60 + 45 * 60; // 2 hr 45 min
I'm drawing a complete blank on how to make it happen. The sensors are stateless so there is no way for me to check if a sensor is online, other than to check timestamps of received data that the sensor posted to the api.
/* FUNCTIONS */
function handleDisconnectAlerts($sensor,$dataset,$users,$settings)
{
end($dataset);
$last_timestamp = $dataset[key($dataset)]['timestamp'];
$now = time();
if($now > $last_timestamp && $now - $last_timestamp > $settings['disconnect_alarm'] * 60)
{
$send_threshold = $settings['disconnect_alarm'] * 60;
$repeat_threshold = $settings['disconnect_alarm_repeat_hours'] * 60 * 60 + $settings['disconnect_alarm_repeat_minutes'] * 60;
//not really sure what to do from here.
}
}

Answer 1

Well, i figured it out myself i guess. The initial check covers the intial interval of 60 * $settings['disconnect_alarm']. From there i just needed to check that an alarm hasn't been sent in $repeat_threshold time. Works like a charm.
function handleDisconnectAlerts($sensor,$dataset,$users,$settings)
{
end($dataset);
$last_timestamp = $dataset[key($dataset)]['timestamp'];
$now = time();
if($now > $last_timestamp && $now - $last_timestamp > $settings['disconnect_alarm'] * 60)
{
$repeat_threshold = $settings['disconnect_alarm_repeat_hours'] * 60 * 60 + $settings['disconnect_alarm_repeat_minutes'] * 60;
$n_sent = R::count('sensoralerts',' timestamp >=:time and field_name="disconnect" and sensor_id=:id ',
[':time'=>$repeat_threshold,':id'=>$sensor['id']]
);
if($n_sent == 0){
multiSendDisconnect($users,$sensor);
}
}
}