Holywells Park has a section of cycle route 51 running through it, linking South East Ipswich to the centre with a pleasant and safe route down to the waterfront.
During Winter, the park is closed at dusk, sometimes as early as 4, meaning that just when the roads are most dangerous (dark and wet) cyclists are forced onto steep and busy routes either along Cliff Lane or up Bishops Hill.
The closures are largely at the request of the Park Friends group. I've spoken to them, and their concerns seem to be largely about what might go on after dark. It's not clear that there is any evidence for this, nor that the current situation of locking the main gates but leaving others would do anything to deter misbehaviour.
Keeping it open as a cycle route would ensure a legitimate presence in the park, and help provide less confident cyclists in the area with a safe route to and from town.
I'd propose either locking later, or for a trial period leaving the park unlocked.