Thanks for the suggestion and in stable radio conditions in a longer event this could work well however in my opinion - as long as one has an active 3G link and can see and post spots, the flexibility given is more applicable when conditions are challenging and variable as they are likely to be.
You also need to bear in mind, of all the stations who have alerted for 0630 UTC 20 % may actually start at 0630, others will be early, some late. Climbing time to all but the easiest summits is a variable depending upon ground and weather conditions. There are those (like mysel) who plan to start later because we have a longer drive to the car park before the climb. So getting to the summit and then thinking “how do I fit into the schedule? can I transmit now or must I wait?” is an extra complication to the activation.
In my experience new activators on summits first tune around to grab the S2S contacts and then find a calling frequency.
With radio conditions being variable, implementing 20 minute windows might stop contacts rather than help them. I think it’s better to activate when the band is open and use the SotaWatch and SmartPhone Apps to see what is out there and let others know that you are on.
A request to all home station chasers (as you normally do), please give priority to S2S contacts taking place and inform the station when there is an S2S call if he/she hasn’t heard it.
A different Idea could be that when an activator calls another summit, at completion of the S2S contact he/she says something like “for other chasers and S2S stations I will be calling CQ in 5 minutes and will spot myself for the frequency”. That’s helps others who wish to contact the calling summit station.
PS Your alert is under 10th. April instead of 10th. March, Guru.