[joosters]

Not sure what you mean? There's a settings->Lock options which has choices from 'immediately, [various times], on restart, and never'.

Or do you mean something like 'you must re-enter your master password for particular sites'?

[dalfonso]

Yes, 'you must re-enter your master password for particular sites'. I liked turning that option on for any e-commerce or highly sensitive sites.

[joosters]

Yeah, no sign of that kind of feature, unfortunately.