Here are two interesting quotes from the Guardian of the Baha’i Faith, Shoghi Effendi—who was known for his tireless efforts to advance the Cause of God during his years as Head of the Faith—about rest and relaxation. The second one I was aware of, but the first one I’d never read before… I always imagined Shoghi Effendi was one of those people who could function with only a few hours of sleep a night.
Regarding your question: there are very few people who can get along without eight hours sleep. If you are not one of those, you should protect your health by sleeping enough. The Guardian himself finds that it impairs his working capacity if he does not try and get a minimum of seven or eight hours.
In a letter written on behalf of Shoghi Effendi, 15 September 1951 to two believers
…you should not neglect your health, but consider it the means which enables you to serve. It — the body — is like a horse which carries the personality and spirit, and as such should be well cared for so it can do its work! You should certainly safeguard your nerves, and force yourself to take time, and not only for prayer and meditation, but for real rest and relaxation….
In a letter written on behalf of Shoghi Effendi, 23 November 1947 to an individual believer
Maybe if I re-read these enough times, it’ll encourage me to get to sleep on time every night :O