So basically to answer your question in your case I'd probably say pick an amount of time that's not too much to get you bogged down in the details, but enough that you pick up on them all, practice timing just the reading, adjust the time as necess…
I rarely did untimed work on RC at all unless it was a blind review type (or just re-doing the section since i was too impatient to wait to see my score). I focused on building up to the full timed section by doing single passages under timed condit…