Did you even read the article?
Valium, for example, has a halftime of about 44 hours in younger people (higher in older people, lower in some others). Forty-four hours after taking a five-milligram dose (5 mg) for example, about 2.5 mg are still in your body.
Your answer was standard textbook but then you throw in a link that contradicts it. Well, thank you for your time.
Can I ask to what depth we are talking here?
Do you take diazepam on a regular basis?
As you take diazepam this often then you will have a more or less constant level of it or it metabolites in your blood. ( you are at a "steady state").
Whilst an increase in partial pressure can increase the fat distribution of drugs - giving rise to an apparent increase in volume of distribution which would elongate the half life - I would conclude that as you are at a steady state already that diving would make only a very small increase to the elimination half life of your diazepam.
Clearly the duration of exposure to pressures above atmospheric is an issue - the longer the exposure the more obvious the effects.
Hope this answers your question.
If not I will be on-line for the next 45 mins or so.