Cheaper to set back heat pump at night or leave at same temp?

Heat pump in question has no emergency heat installed. Location is Phoenix, AZ.
Is it better to turn it down at night or not. User is on a time of use plan from Salt River Project. Peak time in winter starts at 5am but user gets up at 4am and can turn it on then.
Saw this in another group, is it true?

the power company there are two more considerations.
The power rate goes up at 5am so you are likely to be re-heating with more expensive power. Also, a heat pump is less efficient as the outside temperature drops. As it is usually coldest just at dawn, kickiing the systm on then to re-heat is making it try to work when it is at it's least efficient state

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Coldest time is near dawn, so indeed the second item is true. Night-time setback is not encouraged for heat pumps, especially if it would be kicking back on when outside temp is 30 or below.

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snipped-for-privacy@yahoo.com wrote:

It is really difficult to say. Set backs for heat pumps are marginal. Your time of day ratings complicate the thing even more. In general most authorities suggest a minimal set back if any. Local conditions, insulation, efficiency etc all come into play so what works for one may not work for another.
My suggestion is that when the outside temperature is so low as to force it into resistance heating mode, then use the set back. What you want to avoid is the opposite where you are set back during the time when the outside temps allow normal operation only to delay the recovery to the part of the day (generally early morning) when it would be coldest and would be more likely to go into resistance mode.
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Joseph Meehan

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