seeing results?

How long does it take to see results from crunches, pull-ups, push-ups, squats and lunges?

Depends how often you do them.   Once a week - pretty much never.  If you have a serious routine that you do every other day, you should notice pretty quickly that it is getting easier to do more of those activities, after 6 months or so, you'll notice that doing everything else is much easier too because your muscles are much stronger.   If you are looking for results in terms of improved appearance, it really depends on your stats.   If you have a normal BMI already, you'll probably start to see more definition pretty quickly.  If you are overweight, you won't see anything for a long time - but you'll probably notice that your clothes fit differently and better after about 3-6 months.

I saw results very quickly when I first started doing those sorts of exercises 3 times/week. Within two weeks, my starting routine had become too easy and I was able to add sets, reps, and intensity. I also saw a physical improvement within that time period. A certain amount of that is just the "pump" (your muscles filling with blood due to being worked), but you may as well enjoy it anyway. I think I started to see a real difference (actual increased muscle mass) after a month or so.

Just make sure that you continue to challenge yourself. For example, if bodyweight squats are too easy, try doing split sqats or adding some weight.

My BMI is normal. It is on the higher end of normal, but normal nonetheless.

I have been doing these exercises for two weeks and I do them 6 days per week. Once a day, for about 20 to 30 minutes.

I haven't seen any change so far, but I haven't been doing it long enough to see any change anyway.

The nice thing about strength training is that you actually shouldn't be doing it every day - 3 days per week is plenty. If you are doing these exercises 6 days per week, you are not giving your body enough time to rest and repair itself. Try taking a couple days off.