> trial start = trial.trialName.timestamp
Is the correct thing to use. It indicates when the trial object was initiated, that is before the trial object started doing anything else, like executing /ontrialbegin logic or presenting any stimuli.
> trial end = script.elapsed
Whether this indicates when your trial ended depends on how the given trial is set up. Whether this reflects its actual end cannot be answered, since you did not provide any information about that.
> RTFromScriptStart = script.elapsedtime
Same as above.
> Also what is the difference between trial.timestamp and script.elapsed if I use it in a /ontrialbegin?
Already explained above. In practice, you should not see much of a difference. Most of the time they'll be identical.
> Also which of these Inquisit properties would be the closed to the times being saved in the Inquisit audit file?
Cannot be answered based on the information provided.