Before

Setting: the deck (or two) of cards, a list of poker rules

Time needed: 15 minutes distributed throughout the day

During

Each person that returns from a break by the agreed-upon time (be VERY specific!) earns a card. At the end of the day, the person with the best poker hand (or top three) wins a prize. Make the prize something desirable. Otherwise, this trick will not work the next time!
Players can swap cards to try to get the best hand, but they cannot end up with more cards than they earned (no gifting of cards!).

After

Usual or Expected Outcomes: Better punctuality after breaks

Online Tip

This method could be adapted for online use.   The facilitator may shuffle a  pack of cards and then pluck and display a card from the top of the pack for each attendee who turns on their video and greets the facilitator by the agreed time after break and lunch. The attendee will record the number/value of the card plucked on their punctual arrival after break and lunch. The facilitator will also make a note of the cards plucked for each punctual attendee. At the end of the program, the card numbers/values are tallied for each punctual participant, and the one with the highest tally wins a prize, a gift certificate, or a token that is displayed and promptly mailed to them.