Time boundaries

1. Is any of these sentences correct:

a) "Up to a certain point, I had no oipinion about the legalization of cannabis as recreational drug, but after hearing a doctor's stand on this, I now do."

b) "Until a certain point, I had no oipinion about the legalization of cannabis as recreational drug, but after hearing a doctor's stand on this, I now do."

2. And how about theses:

a) "Up to a certain time, I had no oipinion about the legalization of drugs for recreational purposes, but after hearing a doctor's stand on this, I now do."

b) "Until a certain time, I had no oipinion about the legalization of drugs for recreational purposes, but after hearing a doctor's stand on this, I now do."

Note: By this, I mean that before a certain date (or before hearing a certain person), I jad no opinion...

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THANK YOU.