In how much time does telmisartan 20 mg starts acting (showing its effect) in how much time does telmisartan starts working (or starts showing its effect)

Official drug insert. According to boehringer-ingelheim (the manufacturer), most of the effect occurs by two weeks and maximal effect is obtained by 4 weeks.
Telmisartan . Telmisartan is an antihypertensive medication. Usual dosage for an adult is 20mg to 80 mg a day. I would hope that within a week you would notice some improvement in your bp.