You start seeing change pretty much immediately.
I have high BP - was completely unaware until I ended up in A&E, then ortho ward, with suspected broken hip after coming off bike a few years ago. They put me on ramipril - which worked, but side effects didn't agree with me.
Changed meds, and things seemed OK for a while. Side effects disappeared.
Had a routine health MOT a year or so ago, nurse said BP was higher than expected, so they signed me up to "Florence". That's the NHS virtual nurse - they give you a BP machine home, and Flo send you a txt several times a week; you measure your BP and txt it back. She's quite needy - gets quite annoyed if you don't reply within 2 hours and sends you a condescending reminder.
After monitoring for 3 weeks, they changed my meds again. I was measuring BP twice a day, and graphing it, you could see a clear drop where meds changed.
That was the best part of a year ago. I now only measure BP very rarely - maybe once a month.