For Symfony 2.0.x
framework: session: lifetime: 43200 #time in seconds
For Symfony >= 2.1.0
framework: session: cookie_lifetime: 43200 #time in seconds
for sf1.0:
Change the value in apps/appname/config/settings.yml:
all: .settings: timeout: 1800 #session lifetime value in seconds
for sf1.1+:
Add these lines to apps/appname/config/factories.yml:
user: class: myUser param: timeout: 1800 #session lifetime value in seconds