With regard to access to Toton from Derby and Nottingham, I live just over 8 miles from the site of the HS2 station site in south Derby.
At certain times - say in the middle of a Sunday morning - it typically takes about 10 minutes by car from crossing the Erewash Valley line to be walking in my front door, using the A52; however, on a weekday afternoon, it can easily take twice that time.
Regarding Nottingham, one part of the A52 - between Priory Island and the QMC, where its a single carriageway running between the university and Woolaton Park - can itself take 10 minutes by car outside peak times; but even without that congestion, it takes about 20 minutes to the city centre from the Toton overbridge.
For northern Nottingham, the quickest way from Toton will be north up the M1 to Junction 26, then on to the A610; for northern parts of the city (like Top Valley and Bulwell), and on to areas outside the city boundaries like Hucknall, its a trip along the A6002. Then you've got to expect delays when you get to the junction with Hucknall Lane (by the Morrison's); I've known 15 minutes to get through those particular traffic lights late in an afternoon.
So unless there are major investments in roads, it will be extremely difficult to get to/from Toton HS2 station by road.
Toton will be a large station, so a minimum of 10 minutes will be needed from barrier to train departure; then, of course, there's parking.
So by the time you add all of these together, you're easily adding 40 minutes for people in Derby and 60 in Nottingham to get to/from Toton by road at most times of the day.
What happens when you get to London? How many passengers want to finish their journey on the Euston Road? How many will gain a benefit over present connections at St Pancras by changing to CrossRail at OOC or the Northern Line Waterloo branch at Euston?
I've been retired for over 10 years, but that doesn't stop me remembering where I've been going to when I've used MML services to St Pancras; and what has surprised me is that - apart from going to Excel - every journey I've made over the last 25 years or so will be worse going by HS2 and through Euston than St Pancras. Most of my visits to London have either been passing through (onward by Eurostar, Thameslink, or on HS1 domestics), or by Piccadilly or Circle (mostly on the Circle a few stations east but some west to destinations which can't be reached by changing at OOC unless there's another one at Paddington, and - unless major changes to Euston underground are constructed - will require a walk to Euston Square first).
I'm not sure how long it would take me now, but in the past I've walked from my house to Derby station in 40 minutes; walking is the worst case scenario, for I have 8 buses an hour to the station just a couple of minutes walk from my home, and another four each hour if I walk to the next bus stop. One afternoon, I walked off platform 1 at Derby station just as a bus home was arriving, and I was walking into my front door 10 minutes after the train had arrived! That was, of course, a one off; but there's no way that would be possible via Toton - after 10 minutes, I might only just be passing through the barrier!
Regarding rail transits to/from Toton, there used to be a 'Meridian' ECS working between Etches Park and Sheffield which went via the Erewash Valley, and it was allowed 3 minutes between Sheet Stores Junction and Toton Centre; fast 'Meridians' from Derby to Sheet Stores were allowed 7 minutes, so after the Derby station works are finished, a total journey time of a little more than 10 minutes should be possible)
Regarding Nottingham to Toton, in the last timetable there were early morning Northern services between Nottingham and Sheffield (one each way) which were route to/from the Erewash Valley via Toton; these were allowed 13 minutes between Nottingham and Toton Centre
I'm sure most people will look at TOTAL journeys and times, and determine route by convenience, etc; journey time will only come into the equation if there is a SIGNIFICANT journey time reduction, and I believe this won't be achievable between the East Midlands and London using HS2 (apart from people who live in the shadow of the hub station in places like Long Eaton, Chilwell, Toton, Sandiacre, Stapleford, etc.
Of course, I'm looking at this from a personal point of view, so I'm thinking in terms of travelling out from Toton; but why will people travelling in use it? Precedence suggests they won't.
How many people going to watch a cricket match at Trent Bridge or a football match at the City Ground use East Midlands Parkway? Taking the Sheffield "stopper" and a taxi (from EMD) gives a quicker journey time between London and the two sports venues listed than via Nottingham. And the quickest way to Nottingham Uni's main campus is by the same train service and taxi from Long Eaton; but does anyone go that way?
I believe that - despite all of HS2's hype about rebalancing the economy and so on - Toton will only really be of use for some long distance commuters living in the "greater Toton" area; not really sure how big that will be, but it's unlikely to include much of Derby or Nottingham.