Engineering block to commission the new system set to be as follows with Truro being completed first by the looks of it.
27th February - 03rd March: Rail replacement services St. Austell - Penzance and Truro - Falmouth. Trains will run between St. Ives, St. Erth and Penzance and between Plymouth and St. Austell.
04th March - 08th March: Rail replacement services Plymouth to Penzance via. St. Austell and Truro not calling at Liskeard. Also bus replacements Par - Newquay and Truro - Falmouth. Trains will run Plymouth to Liskeard, Plymouth to Gunnislake and also St. Ives to Penzance via. St. Erth.
09th & 10th March: Rail replacement services Plymouth to Penzance as well as the Newquay, Falmouth and Looe branch lines. Trains will run St. Ives to Penzance and also between Plymouth and Gunnislake.
https://www.gwr.com/travel-information/travel-updates/planned-engineering/cornwallDave