Router Clock Synchronisation

I have just experiemced a strange problem and was looking for an explanation. I have six routers each with two interfaces managed. Two of these routers were showing the little exclamation mark saying that the time was not synchronised. On checking inside the routers it appeared that the timezone had not been set correctly by the owner. It was set to UTC but the time was one hour ahead of UTC (ie. on BST). The time has now been set back one hour. However, now all the interfaces on all the routers are showing the exclamation mark. I am writing this from the PC running Netflow Analyzer so I can't imagine that the PC is so overloaded that it is getting 10 minutes behind with processing the flows. Of course I don't even know if this is possible. Is there some kind of queueing mechanism for heavy periods when the flows received come quicker than the CPU and database can cope with? If so, is there a way of displaying what this queue is and where it thinks it is? Is there a way of displaying what Netflow Analyzer is worried about as far as the time on the flows is concerned (ie. why it is displaying the exclamation mark)?