Nurse Missy has 12*(1/3)=<<12*(1/3)=4>>4 special needs patients.
She has 12-4=<<12-4=8>>8 standard care patients.
Special needs patients take 20% longer to serve, which means serving takes 1.2*5=6 minutes per patient.
To serve dinner to all of her standard care patients, it will take 5*8=<<5*8=40>>40 minutes.
To serve dinner to all of her special needs patients, it will take 6*4=<<6*4=24>>24 minutes.
In total, it will take 40+24=<<40+24=64>>64 minutes to serve dinner to all of her patients.
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