In 'hit them' the /t/ is formed, but not* exploded forwards as a [t] sound.
The tip of the tongue starts the /t/ by touching the roof of the mouth just behind the teeth and slides forward down the top teeth. When the tip of the tongue is visible in a mirror the "them" starts.
*This is in normal speech. In very careful speech, there is plosion. (Read more here: Stop consonant - Wikipedia, the free encyclopedia )