You can pause an active (published) campaign at any time without any risk.
To do this, go to the campaign overview, click the “Actions” button to the right of the respective campaign, and then select the option “Unpublish.”
Once the campaign is published again, sending will continue as usual.
This means: Contacts currently in a timer will wait out the remaining time.
Example:
The timer is set to 1 hour. A contact has already been in the timer for 10 minutes when the campaign is set to “Unpublished.”
If the campaign is later published again, the contact will wait the remaining 50 minutes before continuing in the workflow.