When you get to Eersteriver, just ask what train. It either goes back to Strand or Stellies (same platform)! Personally consider catching a Taxi instead. The ones heading to Stellies are safe and more reliable.
Its not on da same platform. U will have to go over the bridge to the other platform. The first two letters of the number denotes the destination eg 32xx is a strand train, 34xx is muldersvlei/stellenbosch. To minimize ur wait, attempt to arrive as close to a 34xx on eersteriver.
* Personally I would rather cycle through to Stellies. You will get there sooner (about 40minutes max from Strand). At least the R44 is amazing.
Also take note that Saturday trains are not guaranteed (or reliable - this is Africa, not Germany). Do not base your plans on the timetables. This is from personal experience.
From the Strand to Cape Town table:
Train 3200 departs Strand at 04:20am and arrives at Eersterivier at 04:45am
Now you have to look at the other table, Cape Town to Strand:
Train 3401 departs Eersterivier at 04:50am and arrives in Stellenbosch at 05:06am
You have to look at both tables as the main route traffic is in opposite directions;
Strand - Stellenbosch - Wellington - Bellville - Cape Town.pdf
Cape Town - Bellvile - Wellington - Stellenbosch - Strand.pdf