If you're looking for a meeting place or a good stop around ½ or halfway between Chalmette and Slidell, you can try South Point, LA, which is about 16 minutes north of Chalmette, or about 15 minutes southwest of Slidell.
About ¼ or a fourth of the way, you can stop at Willow Brook, LA. This is about 7 minutes north of Chalmette.
About ⅓ or a third of the way, you can stop at Little Woods, LA. This is about 11 minutes north of Chalmette.
About ¾ or three fourths of the way, you can stop at North Shore, LA. This is about half an hour northeast of Chalmette, or about 7 minutes southwest of Slidell.
If you drive straight through without stopping at all, the total distance is 28 miles. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 31 minutes.