I have done that leg several times. If you are going outside, out the NW Passage and then straight up to Marco Island, it is about 100 NM. You will have 11-12 hours of daylight at the end of February. If you want to make it before dark, I would push your cruising speed up to 9+ Kts to make it comfortably. I would not want to enter Big Marco Pass after dark.
Or if you want to do say 8.5 Kts, then leave Boca Chica before sunup. I would much rather navigate Boca Chica Channel and the south shore of Key West in the dark than Big Marco.
David