Is Hudayriyat beach open? Yes — daily, but hours differ by beach: the free public beach, Marsana East/West, and the seasonal night beach.

Yes — but "the beach" on Hudayriyat Island actually means a few different things, each running on its own hours. Here's how it breaks down.
Hudayriyat's main public beach is open daily from 7:00 AM until sunset, free to enter, with free swimming and access. After sunset, the standard public beach closes for swimming — that's where the separate night beach takes over.
The two managed beach clubs at Marsana open daily from the early morning, generally from 7–8 AM. These charge an entry fee (which varies by weekday versus weekend, and between the East and West sides) but include sunbeds and, at Marsana East, towels and water.
Every summer, Hudayriyat runs Abu Dhabi's first night beach at Marsana East, letting visitors swim after dark under floodlights. Night Beach timings are:
This runs as a seasonal summer experience rather than year-round, and is a separate swim window from the daytime public beach.
If you're just asking "can I go to the beach on Hudayriyat today" — yes, almost certainly, whatever time of day. What changes is which beach, whether you pay, and whether you can actually swim or just sit on the sand.
Curious how beach access factors into life in a specific Hudayriyat community? Get in touch and I can walk you through which developments sit closest to the free beach versus the paid Marsana clubs.