Summary: Meditation may decrease sleep need, and large amounts of meditation may decrease sleep need drastically. Correlation between total sleep duration & time spent meditating is -0.32 including my meditation retreat data, -0.016 excluding the meditation retreat.

While it may be true that, when doing intensive practice, the need for sleep may go down to perhaps four to six hour or less at a time, try to get at least some sleep every night.

—Daniel Ingram, “Mastering the Core Teachings of the Buddha”, p. 179

Meditation in dreams and lucid dreaming is common in this territory [of the Arising and Passing away]. The need for sleep may be greatly reduced. […] The big difference between the A&P and Equanimity is that this stage is generally ruled by quick cycles, quickly changing frequencies of vibrations, odd physical movements, strange breathing patterns, heady raptures, a decreased need for [...]