(I'm a US native speaker, and not a teacher). I just tried. I personally pronounce two t-like sounds. The "t" in "to" is a normal "t" with a definite little puff of air. What feels important is to create a tiny pause or gap between the "n" in "subsequent" and the "t" in "to." The "t" in "subsequent" is very weak, doesn't create a puff of air, and is hardly there at all, but it does close off the sound and create a little gap or pause. In other words, "subsequendoo" sounds wrong, and "subsequentoo" sounds wrong, while "subsequen, to" sounds right. Pronouncing both T's as normal T's, two of them, with a pause in between is fine, and gives the impression of a person using unusually careful diction.

Duplicated sounds are usually reduced to one sound. Example of double M - "Mom made a pie." In ordinary speech, there is a slightly long M sound [mː] connecting the end of "Mom" to the beginning of "made." The phonetic transcription is as follows: Mo(m) made a pie. [mɑmːeɪdəpaɪ] Similarly a double N reduces for "Ca(n) Nancy ..." and a double L reduces for "Wi(ll) Linda ..." Example of double T - "Get two movies tickets." In rapid speech, the final T of "Get" disappears and "Get two movie tickets" sounds like "Ge two movie tickets." In careful speech, there is a long T sound [tː]. The first "t" stops the air flow, then there is a very short delay, then the second T releases the air flow. Note - The "Mom made a pie" and the "Get two movie tickets" examples came from exercises for reduced speech in English Pronunciation Made Simple by Dale and Poms.

Whenever you have 2 consonants next to each other you can pronounce one of them So one “”s”” is enough to the correct pronunciation

You pronounce both Ts. If you speak quickly enough, people probably won’t even notice if you don’t pronounce one of them, though