This is how to identify default timeout for SSH sessions in High-End Juniper SRX services gateways:
root> show chassis fpc pic-status
node1: //<----- part of name used below
--------------------------------------------------------------------------
Slot 0 Online SPC3 //<----- part of name used below
PIC 0 Online SPU Cp-Flow //<----- part of name used below
PIC 1 Online SPU Flow
Slot 1 Online SPC3
PIC 0 Online SPU Flow
PIC 1 Online SPU Flow
Slot 5 Online SRX5k IOC3 24XGE+6XLG
PIC 0 Online 12x 10GE SFP+
PIC 1 Online 12x 10GE SFP+
PIC 2 Offline 3x 40GE QSFP+
PIC 3 Offline 3x 40GE QSFP+
{primary:node1}
root> request pfe execute target tnp tnp-name node1.fpc0.pic0 command "show usp app-def tcp"
================ node1.fpc0.pic0 ================
SENT: Ukern command: show usp app-def tcp
tcp port=0, appl_name=junos-tcp-any, service type=0, alg id=0, timeout=1800
tcp port=20, appl_name=junos-ftp-data, service type=0, alg id=79, timeout=1800
tcp port=21, appl_name=junos-ftp, service type=1, alg id=1, timeout=1800
tcp port=22, appl_name=junos-ssh, service type=22, alg id=0, timeout=1800 // <------ default SSH timeout is 30 minutes (1800 seconds)
tcp port=23, appl_name=junos-telnet, service type=10, alg id=0, timeout=1800
tcp port=25, appl_name=junos-smtp, service type=7, alg id=0, timeout=1800
//further output omitted
