In article et,
DaveC wrote:

How can I delay the de-energizing of these relays? 5 minutes
without power is OK.

Use something like this maybe. View in fixed width font.
____
+---------+ +------|AC +DC|---+-----+ +----Out
| | | | | _|_ |
)||( | Bridge | +|C | | o |
120Vac )||(18Vac |Rectifier| === | RL|----|N/O
)||( | | | |_ _| o |
| | | | | | |
+---------+ +------|AC____-DC|---+-----+ +----Out

A 120:18V transformer on the mains, bridge rectifier,
capacitor smoothing, and 24V comms relay.

Relays have an On/Off hysteresis. Once it has been
energised, a 24V comms relay will not then release
until the voltage has reduced to below about 8V.

24V sinking to 8V is not far off T = R*C.

A standard 24Vdc high sensitivity comms relay has a coil
resistance of about 2900 ohms. If C= 47000uF then the
the relay will be held closed for about 136 secs after a
mains failure.

A 47000uF (at 35vdc working) is not cheap, and the thing
is a little clunky, but easy to put together and not much
to go wrong.

--
Tony Williams.