Companion II and Enterprise "S" use the MCU standby pin.
Super Enterprise uses an internal standby bit (Leonardo/Renaisance, Super Nova do it this way too). I doubt it can be done with a timer.

map(0x0000, 0x0014).m(m_maincpu, FUNC(hd6301y0_cpu_device::m6801_io));
That's the range for V1, try 0x21.

Also: hd6301y_io, not m6801_io