All that means is that the router itself has been up for 55 hours. The connection time up is given by this:
Your last re-connection to the WAN was 20 mins ago. You should be able to see this in the router's log. Sometimes a re-connection resets the System Up Time and sometimes it doesn't. I suspect it's the diff between a re-sync at the exchange and a LCP/CHAPS event at the ISP's authentication server, but I'm still trying to suss it out.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 17 Meg Untweaked 19 Meg Tweaked WBC