The Defers will create a lag, but I am concerned that you have a circular reference. In otherwords, ATO relies on ATO_Failsafe which relies on ATO. This should be avoided by referencing the basic trigger, in this case switch1.
And yes, the Defer will interfere with the failsafe. A Defer...OFF will apply to all OFF conditions, similar with Defer..ON. Also, Defer (and Min Time) are always resolved last regardless of position. I prefer to place them last just as a reminder.
There is an alternative that combines a limited runtime with float control.
[ATO_Allow]
OSC 00:00/03:00/57:00 Then ON
[ATO]
Fallback OFF
Set OFF
If Switch1 CLOSED Then ON
If Outlet Maintenance = ON Then OFF
If Outlet ATO_Allow = OFF Then OFF
If pH > 8:50 Then OFF
Defer 00:10 Then ON
ATO_Allow sets up a repeating 'window' that limits the runtime to three minutes out of every hour. Adjust the last parameter as necessary, ie set to 117:00 for every two hours, etc. But, the ATO will run as necessary within that window.
I also recommend configuring the float so that if disconnected, the safest condition occurs. The Apex switches default to OPEN, so in this case the ATO would stay OFF.
Use just enough Defer duration to filter out any noise, but not so much that it lags too much from an accurate sump level. A Defer...OFF would cause the sump to overfill.
Todd