If you lived close by the escalator then 40 mins to Kowloon Station platform would be pretty much worst case. If you walk down the escalator from, say, Mosque Street, then you'd be on the platform in HK Station within 15 mins of getting on the escalator. You'll wait an average of no more than 4-5 mins for a train, and be on Kowloon Station platform 3 mins later.
Asuuming it's about the same time to your office from the platform as from the taxi drop-off then I don't think you'd save much more than 5, or at most 10, mins by getting a taxi. Over $100 seems quite a large amount to pay every day for 5 minutes more in bed.