Length: About 15 km (9.3 miles), with options to lengthen. Toughness: 1/10
10:39 Reading train from Waterloo (Vauxhall 10:43, Clapham Jct 10:49, Putney 10:53), arriving Richmond (in TFL Zone 4) at 10:58. You can also travel to Richmond on branches of the Overground or District line: use the TFL Journey Planner to arrive by 11am. Meet upstairs in the ticket hall.
You can return from either Putney Bridge (District line, Zone 2) or Putney mainline station (Zones 2/3; seven trains an hour to Waterloo). NB. There's a rugby international at Twickenham (England v Italy at 3pm), so the mainline trains will be crowded after 5pm.
The introduction to this walk describes it as “a fine winter walk” along “a pretty section of the Thames Path”. To minimise walking towards the low winter sun (fat chance!) I've chosen to do it in reverse, ie. heading downriver from Richmond. In this direction the GPS route sticks to the south bank throughout, but if you check the walk notes you'll see the bridges where it's suggested you could switch to the other bank. In particular there are more features along the north bank after Barnes Railway Bridge, where you'd also have the option of detouring off the Thames Path to Chiswick House, Fulham Palace, etc.
If you're feeling peckish by the time you reach Barnes (after 9 km) you might well be tempted by one of its large riverside pubs, but the notes actually suggest doing the walk without stopping. At the end there are two large pubs on the south bank as you approach Putney Bridge, plus a Wetherspoon's in the remodelled Putney Wharf Tower just beyond it (The Rocket). There are also several cafés and other eateries on and around Putney High Street.
You'll hardly need any directions for this walk, but the L=swc.390 page has some useful information about the features along the way. NB. As this is part of a series of walks along the Thames Path the GPS starts by taking you to Richmond Bridge, but there is a shorter (and quieter) route to the river via the green.
If you might want to switch to the north bank at Barnes Bridge, the Walk #261 page has a suggested route via Chiswick House.