Push a stream of air from your throat through your open mouth. No tongue or lip contact.

Americans pronounce halftime as HAF-tahym (/ˈhæfˌtaɪm/). Stress falls on the first syllable — keep everything else short and quick. You'll hear it in sentences like "The halftime show featured a famous pop singer".
Record yourself saying "halftime" and play it back. The mic stays on your device — nothing's uploaded.
2 syllables, 6 sounds. Tap a syllable to jump to its row, then explore each sound's mouth shape and how it's made.
Push a stream of air from your throat through your open mouth. No tongue or lip contact.

Drop the jaw noticeably. Keep the body of the tongue low and forward, and don't let the back of the tongue raise toward the soft palate. Pull the lip corners back slightly, almost a starting smile.

Lift your bottom lip to touch the very bottom of your top front teeth. Blow air through this contact point without voicing.

Touch the tip or front edge of your tongue to the roof of your mouth just behind your teeth. Keep your jaw relaxed. Stop the air, then release with a puff.

Start with your jaw open wide and your tongue resting low and flat. Glide the front of your tongue up toward the roof of your mouth as your jaw closes halfway.
Press your lips together. Air flows through your nose. Vocal cords vibrate.

The textbook way isn't wrong — it's just not how anyone actually says it.
Stress falls on the first syllable, not the others. Stretch HAF — keep everything else short and quick.