Rower,
How far is it from Derby to LE & how long to cycle 'twixt the two stations.
I might use the train 
Approx 9 miles. Including faffage, meeting-up, contingency and general padding (you can tell I work with Railway timetables
), an hour ought to be about right.
Forgive my ignorance, but how much would that cut off the overall route?
Nothing. It just means you do the 9-mile feeder at the start of the ride, rather than at the end. The most cyclist-friendly (avoiding busy roads, traffic, contours) route from the Holly Bush at Makeney to Long Eaton station goes within a gnat's crotchet of Derby station. I'd be happy to do that bit twice if need be - i.e. do the feeder ride from Derby to Long Eaton, then do the ride, drop some participants off at Derby station, then continue on through to Long Eaton for the official end. (Then back - on the train if I'm feeling a little tired by then!)
Route from Derby station to Long Eaton:
Out of station at Pride Park entrance
1st Left past roundhouse
L onto Cyclepath
Under flyover, sharp R to join riverside path.
Follow riverside path (4 miles) to Borrowash
L onto B5010 Station Road Borrowash
R onto A6005 Derby Road
R (to remain on A6005) Signed Draycott
R in Draycott (actually straight on as main road turns left) signed Sawley
L in Sawley onto Tamworth Road - leads to Long Eaton Station.
Completely flat. And this is from someone who has to swallow when they step off a kerb, to equalise the pressures. (Oh, alright, one or two railway bridges to go up-and-over. No more than 20m climb TOTAL in 9 miles.)
Route from Holly Bush to Derby station:
Out of pub - Left onto Duffield Bank
L onto Eaton Bank
R in Little Eaton onto cyclepath alongside Alfreton Road
Follow path - cross A38 on Cycle traffic lights
Cyclepath alongside Alfreton Road (A61) to Pektron Island
R onto Alfreton Road
R into Haslams Lane (signed Rugby Club)
L onto Folly Lane
SO onto Cyclepath through Chester Green (wave at Rowing Club on other side of river)
SO into City Road
R then 2nd L into Phoenix Street
R onto Derwent Street
L onto Riverside cyclepath BEFORE crossing river
Follow Riverside path until Derby Evening Telegraph offices
R over bridge
L onto riverside cycle path
After bridge under railway, bear R for cyclepath to station.
R past Roundhouse (Derby College) - and the Pride Park entrance to the station is on R.
Hope that all helps.
