you can either add a sample number before the table lookup (left inlet) with +~ or use the right inlet, which allows for greater precision (int precision) when added to the left inlet rather than just float precision (which is 24 bits at a 32 bit depth) for the index though it can only be specified by messages at block boundaries. according to the help file, you should always start reading from tabread4~ at sample value 1 because of the wraparound
if you change the start point while it is reading the array you'll get a doppler shift or popping, you could use samphold~ after the phasor~ in order to only get values when it starts over. If you're going for the doppler shift (like adding an osc~) it's called phase modulation I think
the example at the bottom of the page does seem to have an offset control in seconds (converted to samples)
tabread4~ and tabread~ are basic table lookup, so you need to provide these kinds of modifications yourself. a useful external with more features is loop~