Mass Effect: When is it too late to rescue Liara?

As far as I know it is only affected by the main storyline, that is the trigger for the romance conversations. Doing a single side mission shouldn't have an effect on your ability to romance her.

On the other hand if you wait until the very last possible moment to free her she thinks you are a hallucination and says some rather funny stuff, eventually asking you to free her if you are real and if you are a hallucination to please go away as she is tired of talking to herself.

In the ME storyline all "timed' events are dependent on missions done, for example in ME2 you need to go somewhere to save some people, if you wait 10 minutes but do 1 mission then 1/2 of them die, if you wait 2 hours and collect lots of resources and get all possible upgrades but do no missions then the entire group survives.

I'm playing the Playstation 3 version.

I just became a Spectre and am now checking out the numerous planets you can explore. I heard, though, that if you take too long to find Liara T'Soni, the cutscene where you find her will be different and you may not be able to romance her.

*How long is too long?*

Is it based on an actual time limit, or is it based on what order you do the planets? I landed on one side-quest planet (the one in Hades Gamma where you find out what happened to a survey team that disappeared). Does that count toward the delay, or does the delay only apply to the main locations (Feros, Noveria, Virmire)?