The park have recently announced that this year's Mardi Gras event will be taking place from 29th March to 14th April, as opposed to in May. They also currently have an early bird ticket offer, where if you book for a visit before 25th April by the start of March, your entrance ticket costs £29.
I'd say both of those show that it won't open in April (as it's the park's way of getting people to visit).
May still feels possible. I'd say track will completed by mid-March. Given there's already been a lot of electrical work, 2 months for testing, landscaping, styling (which has also already started) feels plausible.
So yeah, I'm saying mid-to-late May is likely the aim at the moment.