it is random with respect to time, though obviously you wont get a +12 TC on the first hand dealt so there are some limitations like that. see
this page from QFIT's ebook. basically you can expect "mini" random distributions around 0 but with different min/max TCs for each "mini" distribution depending on depth level of the pack. so for example, using the first picture in that link, 1 deck into a 6D shoe, you might see a normal TC distribution from -8 to 8, where the TC randomly varies between those 2 endpoints within 1D's worth of play. but it is still random.
if it were anything else but random you would be able to take advantage of it....