ms/j2ee_reconnect_timeout_p2 is a SAP Parameter attribute which is used to control Reconnect timeout for phase 2 information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
Time limit for connection setup after message server restart in
reconnect phase 2
See SAP Parameter Documentation for full SAP documentation for this profile parameter.