Usually, I do yoga (pranayam and some asnas) around 1 hour and immediate after this I also do some set of workouts like leg raise, push ups, mountain climbers etc. Is that okay or should I have some time gap between these two activities?
Yes, it's okay to perform other body weight exercises right after yoga. P90X has a video on cardio; the video starts with about 15 mins of yoga (as warmup exercises), after which it moves into Kempo moves for about 15 mins. It then goes into cardio section and finally ends the session with 15 mins of body core exercises. That basically answers your question.
However, an hour of yoga followed by body weight exercises seems to be backward. Since those yoga exercises are designed to have a calming effect on the body, it makes more sense to start heavy (body weight exercises) and finish light (yoga). This should give you a better workout than your current situation.
Hopefully, this helps.
Now, give me some ashtanga salutations :).
The answer very much depends on what exactly your asana practice consists of, and what your goals are.
Yoga asana practices usually consist of active static stretching and passive stretching. There is very little dynamic stretching in yoga. This is important for you, because passive stretching does not fit into the beginning of a workout. So if your asana practice consists of mainly passive stretching, then it is better to do your asana practice after your conditioning routine. However, if active static stretching is the main focus of your asana practice, then, it may not hurt to do it in the very beginning. However, dynamic stretches fit much better to the beginning of a workout, which a usual asana practice can not provide. For further reading on the types of stretching and their effect, refer to Stretching Scientifically by Thomas Kurz.
Strength wise, asana styles can vary a lot, from very light practices to really hard ones. However, the primary aim of asana practice is to enjoy all the benefits of increased circulation, without putting extreme stress on the body. So after a yogi has finished with his/her asana practice, he or she is well prepared for pranayama practice and long kumbakhas (breath retention exercises). You may not be able to perform long breath retentions after an exhausting workout (either asana or conditioning).
To conclude: as you can see, if you are serious about both yoga practice and conditioning, it is better to put them in completely different workouts (different days, or morning/evening splits are fine). Otherwise, it may be ok to do them together, but note, that 1. asana will probably reduce the efficiency of conditioning, and 2. very high intensity conditioning will make pranayama more difficult.
I think that the best option for you depends on whether you want to focus more on your conditioning, or yoga goals. If yoga is more important to you, then do that first, but try to do more active stretching than passive in your asana. If you want to focus more on conditioning, do that first, go as hard as you can, then follow up with asanas of mainly passive stretching, then some very easy pranayama.
I would also add the same caution people have started making in regards to stretching before running, namely that if you over-stretch, you may make the tendons and muscles looser and more likely to be injured if you heavily exert them. Proper yoga, I am sure, does not strain the muscles and joints, but many people get competitive about getting deeper into the pose than the person beside them.