For Sierra Leone in 1957-1962, the standard time was defined in the Alteration of Time Ordinance, 1932 (as amended in 1946, renamed to Local Time Ordinance in 1960 and Local Time Act in 1961). It was unamended throughout that period.
Alphabetical Index of the Legislation in force on the 31st day of December, 1957...1963
https://books.google.com/books?id=lvQ-AQAAIAAJ&pg=RA2-PA49
https://books.google.com/books?id=4fQ-AQAAIAAJ&pg=RA2-PA50
https://books.google.com/books?id=p_U-AQAAIAAJ&pg=RA2-PA55
https://books.google.com/books?id=JPY-AQAAIAAJ&pg=RA3-PA37
https://books.google.com/books?id=7vY-AQAAIAAJ&pg=RA3-PA41
https://books.google.com/books?id=W_c-AQAAIAAJ&pg=RA3-PA44
https://books.google.com/books?id=9vk-AQAAIAAJ&pg=RA1-PA47
Also, the "Standard Times" section of The Air Almanac and The Nautical Almanac in that period did not indicate any DST for Sierra Leone.
The Air Almanac:
1957 Mar (1958.5-8)
https://books.google.com/books?id=atUgEBQtHtkC&pg=SL1-PA20
1957 Jul (1958.9-12)
https://books.google.com/books?id=0KY2rR6duhwC&pg=SL1-PA20
1957 Nov (1959.1-4)
https://books.google.com/books?id=WYAs3WA6udMC&pg=SL1-PA20
1958 Mar (1959.5-8)
https://books.google.com/books?id=oGS4QZuJJg0C&pg=SL1-PA20
1958 Aug (1959.9-12)
https://books.google.com/books?id=6G-9_eF5rksC&pg=SL1-PA20
1958 Nov (1960.1-4)
https://books.google.com/books?id=ZpwPAQAAIAAJ&pg=PA121
1959 Mar (1960.5-8)
https://books.google.com/books?id=yUeLN7rEYX4C&pg=SL1-PA20
1959 Jul (1960.9-12)
https://books.google.com/books?id=lYjcV7OhT60C&pg=SL1-PA20
1959 Nov (1961.1-4)
https://books.google.com/books?id=pyqItzbOn0QC&pg=SL1-PA20
1960 Apr (1961.5-8)
https://books.google.com/books?id=ikbWuVALgxoC&pg=SL1-PA20
1960 Aug (1961.9-12)
https://books.google.com/books?id=vJ0PAQAAIAAJ&pg=SL1-PA20
1960 Nov (1962.1-4)
https://books.google.com/books?id=bVgtWM6kPZUC&pg=SL1-PA20
1961 Mar (1962.5-8)
https://books.google.com/books?id=W2nItAul4g0C&pg=SL1-PA20
1961 Aug (1962.9-12)
https://books.google.com/books?id=kFQiAQAAIAAJ&pg=RA4-PA20
1962 Jan (1963.1-4)
https://books.google.com/books?id=Ftxx170J--AC&pg=SL1-PA20
1962 May (1963.5-8)
https://books.google.com/books?id=VAxyCZRB2EcC&pg=SL1-PA20
1962 Sep (1963.9-12)
https://books.google.com/books?id=Y8361ReDPRYC&pg=SL1-PA20
1963 Jan (1964.1-4)
https://books.google.com/books?id=tBLVzhTj_5UC&pg=SL1-PA20
The Nautical Almanac:
1957 Dec (1960)
https://books.google.com/books?id=PrZPAQAAMAAJ&pg=PA264
1958 Dec (1961)
https://books.google.com/books?id=UrZPAQAAMAAJ&pg=PA264
1959 Dec (1962)
https://books.google.com/books?id=hbZPAQAAMAAJ&pg=PA264
1960 Oct (1963)
https://books.google.com/books?id=urZPAQAAMAAJ&pg=PA264
1961 Oct (1964)
https://books.google.com/books?id=1LZPAQAAMAAJ&pg=PA264
1962 Sep (1965)
https://books.google.com/books?id=67ZPAQAAMAAJ&pg=PA264