I really enjoy meditating right before sleep, and it’s so calming and an easy way to fall asleep, that it didn’t take me much time at all to make it a habit. I use Headspace, the free version. They have lots of useful meditations for free, they have a 5min wind-down meditation, some “sleepcasts” and “soundscape” sounds for going to sleep. They also have Basics, 10 sessions that teach you the basic skills of meditating and you can choose 3, 5 or 10min length for each session. Good luck!
However much time you need. I think you can make a meditation habit from a minutes to an hour. It depends on your needs and skill. If you are new to meditation or just incredibly busy, one minute of meditation can be very helpful. Some people can’t imagine sitting in complete silence doing nothing for a full 60 seconds, so for those people one minute is a lot. I usually do between 5-15 minutes in the evening to prepare for bed.