If you still have the seed packets take a look to see how many days to germination. Once you know how long before you should see growth, give them an extra week before giving up on them. I don't know what 'night flowers' are. I've never heard that term but I'm wondering if you might be growing moonflower aka Ipomoea alba. Do you have the botanical name of this plant? Is this a vine that has white flowers that bloom at night? If so, these seeds can take a long time to germinate, especially if you didn't scarify (nick) the seed to aid in germination.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.