Having a full-time job and studying at the same time for certifications can be a challenge, but kudos to you for taking up the challenge! One of the best ways to deal with such a situation, where time is limited, is to put together a schedule, as you so wisely have done. The second thing you should do is make sure to make the best of that time by planning the topics you will be covering. Go over the issues and topics that you are the least familiar with and leave the more familiar topics for last. Sometimes some labs may need more than 2 hours to complete fully, so you may want to put aside some extra time occasionally to deal with those.
Now whether or not that is enough really depends upon how quickly you pick things up, and how knowledgeable you already are. But in general, two hours a day is a very good rate, and if you keep it up, you will be ready for certification…
It also depends upon what certification you’re going for CCNA level you should be up to speed in a couple of months. WIth CCNP, at that rate it may take 6 or more months. For CCIE a year or more. But again, these are just guidelines, it may take much less or much more depending on you.
As @sen2diwakar mentioned, it also depends on the topics you learn that are relevant to your job.
I hope that gives you a clearer picture of how to proceed. In any case, for whatever else you need, you know where to find us!
I hope this has been helpful!