It is right there in the link you provided:

> The file naming convention of SLSTR products (see this document for more details) is identified by the sequence of fields described below:

>MMM_SL_L_TTTTTT_yyyymmddThhmmss_YYYYMMDDTHHMMSS_YYYYMMDDTHHMMSS_[instance ID]_GGG_[class ID].SEN3

>[...]

> yyyymmddThhmmss is the sensing start time
> 
> YYYYMMDDTHHMMSS is the sensing stop time
> 
> YYYYMMDDTHHMMSS is the product creation date

>[...]