Some more work on the history of legal time in the Channel Islands (some way still to go before the information for the Crown Dependencies is as complete as that for the UK, though).... I found this, relating to the adoption of GMT in Guernsey, in the published "Recueil D'Ordonnances de la Cour Royale de l'Ile de Guernesey", Tome V, 1901-1931, in Cambridge University Library. The library doesn't have a correspoding series for Jersey, so I don't yet have the corresponding 1898 law for Jersey. (Likewise, I have yet to check the 1883 law of the Isle of Man mentioned in the europe file, and nor do I know whether this law of Guernsey would cover Alderney or Sark, which at least nowadays are part of the Bailiwick of Guernsey, but which made some of their own summer-time legislation in World War 1.)
From the World War 2 period, when the Channel Islands, under German occupation, may well have used a different time from that in the UK, I have references to "The Defence (Channel Islands) Regulations, 1944", with marginal titles "Advance of time" and "Change of time", being registered on the records of Guernsey; these regulations having been made by the officer in command of the armed forces in the Channel Islands under powers given by The Emergency Powers (Channel Islands) Order in Council, 1944 (S.R. & O. 1944 No. 1483), but apparently not themselves included in the series of UK Statutory Rules and Orders.
Ordonnance réglant l'heure légale. La Cour, en renouvelant les dispositions de l'Ordonnance provisoire réglant l'heure légale passée aux Chefs-Plaids d'après Pâques tenus le 19 avril 1909 et renouvelée par l'Ordonnance provisoire passée aux Chefs-Plaids d'aprés Pâques tenus le 31 mars 1913, ouïes les conclusions des Officiers du Roi a ordonné et ordonne :- Vu la délibération des États en date du 7 avril 1909. La Cour, ouïes les conclusions des Officiers du Roi, a ordonné et ordonne :- ARTICLE UNIQUE ^ L'heure légale en cette Île est l'heure temps moyen de Greenwich. | [marginal note: L'heure légale temps moyen de Greenwich.] -- Joseph S. Myers jsm28@cam.ac.uk