Guyana

British Guiana/Guyana adopted GMT-4 on 1911-08-01 , GMT-3:75 on 1915-03-01, GMT-3 on 1975-08-01 and GMT-4 on 1992-03-29.

The Official Gazette of British Guiana. (New Series.) Vol. XL. July to December, 1915, p 1547
https://books.google.com/books?id=5-5CAQAAMAAJ&pg=SA1-PA547

Interpretation and general clauses (Amendment) Act 1975 (Act No. 27 of 1975) [1975-07-31]
https://parliament.gov.gy/documents/acts/10923-act_no._27_of_1975_-_interpretation_and_general_clauses_(amendment)_act_1975.pdf

Interpretation and general clauses (Amendment) Act 1992 (Act No. 6 of 1992) [1992-04-18]
https://parliament.gov.gy/documents/acts/5885-6_of_1992_interpretation_and_general_clauses_(amendment)_act_1992.pdf

Circular No. 10/1992 dated 1992-03-30
https://dps.gov.gy/wp-content/uploads/2018/12/1992-03-20-Circular-010.pdf