Well for starters, it won't open without a light. And secondly, sometimes it will take a few days, sometimes it won't. I've had some that opened the next day and some that took a couple weeks, so be patient. If its still not opening in a 3-5 days in the light, maybe try moving it to an area with different flow and light. They like low flow and lower lighting, so if its getting more than it likes, it will stay shut.