(a) The draw of the Lansing Island Bridge, mile 0.7, at Indian Harbour Beach, shall open on signal, except that from 10 p.m. to 6 a.m., daily, the draw need not open for the passage of vessels and will be untended.

(b) The draw of the Tortoise Island bridge, mile 2.6, shall open on signal; except that from 10 p.m. to 6 a.m. from Sunday evening through Friday morning, the draw shall open on signal if at least 2 hours advance notice is given. From 10 p.m. to 6 a.m. on Friday and Saturday and on evenings immediately preceding Federal holidays, the draw shall open on signal if at least 30 minutes advance notice is given.