Not sure this is possible without using flow but hopefully..
Have an approval forms, after a manager submits the form it is approved by the first tier approver, on that approval an email is then sent to a second tier approver, on this approval an email is sent to our HR department.
What i am after is, if the second tier does not approver/decline the request after 72 hours that an email is sent straight to the HR department.
Looking at a timed email i guess but is this possible using PowerApps only?
(side note my form does not use Flow to do this approval form at all)
I would just convert the entire approval process to Power Automate. Power Apps is primarily a declarative language and has trouble doing procedures. Power Automate is designed to be procedural. Its the better tool for what you are trying to do.
Unfortunately that's not possible, my company do not want to use flow.
Is it possible to do set a timer to send the email? Or is it just not doable without flow?
You'll need to track the status in the item and use a timer to check it. Then send the approval when the timer kicks off and the status is correct. It can probably be done, but it will be a very difficult build. Its just not the right tool for the job.