You can only dive Town Pier at night. My personal opinion is that Salt Pier is best in the morning. I'm not clear on what you're asking, you personally won't be able to get permission, you have to go through a diveop. So it's up to them/their schedules.
Bari Reef between Sand Dollar Condos and Den Laman is another option. Easy dock entry, it's the reef with the most counted fish species in the Caribbean. Bonaire Dive & Adventure is the on-site diveop there, it's their facilities you use.
As on Curacao, you'll need to make prior arrangements to get tanks after hours. Most diveops close around 5PM or so. Some places may leave a tank out for you. I think Buddy's drive-thru is an exception, they may be open later - anyone know?