Subtract teaching and setup time first
In a 45-minute slot, reserve ten minutes for setup and a practice turn and five minutes for putting things away. That leaves about thirty minutes for actual play. A game advertised for 45 minutes may not fit this group, especially if several people have never played or the first round runs slowly.
Ask what kind of participation people want
Someone may enjoy solving a puzzle with others but dislike competing in teams. Another person may want a game where conversation can continue between turns. Ask before assigning roles. Check player count, required reading or language, and whether an available seat or surface works for everyone.
Agree on a natural end
Set up one sample turn before starting the full game. If someone does not enjoy the rules, offer a role such as scorekeeper only if they want it. Keep a simpler activity ready for anyone who would rather join differently.
Explain what a turn looks like and how the game ends. If time is short, use a shorter variant only if it actually works under the game's instructions. Offer a completely different game for the next round without making the newcomer feel responsible for changing the plan. Save the longer choice for an evening with room to learn it.