How to turn off triggers for a specific period

Create user accounts for all the receivers, add corresponding media entries (emails) to them. Configure actions as usual, but place all of these users in a common usergroup that has "Frontend access" set to "Disabled" - this way they will be able to receive notifications, but not log into the frontend.

Alternatively, have a single user account with multiple user media entries for all the email addresses.

Your question is not 100% clear, so I've covered both possibilities:

If you want to check whether data is not arriving from the Zabbix agent, use the nodata function.

Returns:
1 - if no data received during period of time in seconds. The period should not be less than 30 seconds.
0 - otherwise

For example, a trigger which will fire if no data was received for 10 minutes:

{mysql.query.nodata(600)}=1

If you want to check whether the value has not changed, use delta.

Returns the difference between the maximum and minimum values in a period ('max()' minus 'min()'). The period is set in seconds or as a number of collected values (preceded by a # hash mark) in the first parameter.

For example, a trigger which will fire if the value has not changed for 10 minutes:

{mysql.query.delta(600)}=0

Finally, you probably want to rename your item. mysql.query is very generic, and is already used by common MySQL templates. Something like aggregator.highest_click_id might be more appropriate.