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
[...]
