I have a major issue that I just cant seem to make come to an end!

I took everyone's advice on how to get chit chatty parents out at pick up. I tried every single thing that you wonderful ladies suggested and it didn't work.
I even set an alarm on my phone and was like "ops that's an important call I have to go" they continued talking and wait told me to get the call as she would wait!
I had one mom lingering around talking for 30 mins!!!!!! I don't mind talking for 5 but come on! The thought of having to talk to someone after a long day makes me for grumpy every morning ! I even tried having all the lights off and I have one parent in particular who has nothing but time bc shes waiting to catch a bus. Being sweet will not work so I need to be firm but how do I do that without sounding mean? Please help