Length: 18 km (11.2 miles). Toughness: 2/10
10:20 Ramsgate train from Victoria† (non-stop to Sevenoaks 10:55), arriving Paddock Wood at 11:18. Buy a return to Yalding (or Wateringbury if you might want to extend the walk: see below).
† There are no trains from Charing X and Waterloo East because of engineering works.
Trains back from Yalding are hourly at xx:11 (xx:08 from Wateringbury), changing at Paddock Wood for Victoria.
This is an easy walk in the Medway valley, with a large chunk of it alongside the river. You'll reach Twyford Bridge before 1pm, with a choice of the “bistro-style café” on Teapot Island or the Boathouse across the river for a pub lunch. The afternoon is a loop out through Yalding village to Hunton, returning to the same places at Twyford Bridge for tea. You could then get to Yalding station via the main road but a slightly longer alternative route would take you through a community orchard, where there might be a few early windfalls to be had.
Optional Extension: If it's a nice day you could carry on alongside the Medway to Wateringbury station, an extra 40 minutes or so.
You'll need to bring the directions from the L=swc.338 page.