Some useful tools will help you in planning your trip/walk, and I'm sure I'm forgetting some ..
SotaMaps Tracking page
see if someone uploaded a track for the summits you were thinking of
Check the summits database at http://www.sota.org.uk/Associations
To start off, select a summit that has the most activations, they are usually the easier ones (with exceptions of course).
See if there are any resources added for the summit (ususally labeled "Access info").
If not, see who last activated the summit, find their email on qrz.com and ask them for more info, on where to park, where to operate, ...and if there are any trees !
I have never been without reply from any of the activators I wrote to.
Most will actually give you more info than you asked for ...
(Note : I wouldn't select a summit that has not been activated before as your first target. There is always a reason .. no access road, private property, too difficult or too dangerous ...)
Now for your question how to determine ETA, use one of the many mapping sites, just as an example this one :
On the right there is a "Layers" symbol (4th from the top), select the "Bicycle map".
Find your summit (clicking on the link on the Summits page will take you there too).
Supposing you can see the track you want to follow, click right on the start and select "Directions from", then the same for the target, but select "Directions to".
On the left then, use the drop-down box to select "Walking (Mapzen)"
Distance and time will be calculated, but in my experience, multiply that time by 3 !
(maybe I'm a slow walker, or I stop too often to take pictures )
Many other tools exist, like https://www.gaiagps.com/map/
and others, but this should get you started.
Good luck es 73
Luc ON7DQ (and KF0CR when I'm in Springfield, MO)