SGB is available for trading in the secondary market immediately after 15-20 days of issuance.
SGB naming scheme is simple, for example, take SGBSEP28 bond.
Here ‘SGB’ stands for Sovereign Gold Bond, ‘SEP’ is the month and ‘28’ is SGB’s maturity year.
SGB’s mature after 8 years from the date of issuance, so the above mentioned bond ‘SGBSEP28’, was issued in September 2020 and will mature in September 2028. You can check the list of all the SGB’s which are listed and are trading on exchanges here.
To know more about SGB, you can read this post.