"All the time" or "constantly."
It's derived from the term 24/7. 24/7 is actually a fraction, so we can calculate it in its repeating decimal form. 24/7=3.428571...
"3.4" is just used because it's much easier to type and say than the previously mentioned decimal equivalent.
Joe: OH NOES I GOTS TEH SHITZ!!!!111 I think im SICK AGAIN! =-o :-\
Phil: You're sick 3.4, you really need to go to the doctor... or go to bed at a normal time... OR stop eating fast food every day...