Hi Stallie,
For us it is 90 minutes flying time at EOI- speed, giving us a distance of 671 miles til EET (that doesn't have to be your departure point BTW. For MEL-LAX we sometimes use EET predicated on BNE + 671 miles along track). Some operators use 60 minutes, and it can indeed simetimes be advantageous to get into your EDTO segment sooner, rather than later.
And you're right about the use of non-EDTO - as long as there is an operational airport THERE (within 60 minutes EOI flying time), it matters not whether it is socked in in fog.
Cheers