How many Tylenol #4 tab can u take in 24 hour period? what is MAX in 24hrs

I have been taking 2 tabs every 4 hours. I have had 8 back surgerys and 4 fusions and suffer with cronic back pain. I take a total 12 a day. My pharmist said I could take up to 12 a day and a nurse said u are only to take 1every 4 hours not to exceed 6 a day. I am confused because my pharmist says different???

Please let me know the max per 24 hour period or where I can go to find out.