Notsure how it could have happened without user intervention but you could check that these network services arent loading by the "delayed start" option in Control Panel > Administrative tools > Services. (or type services into to control panel and use the one with the Cog icon.
Failing that perhaps it's just general startup degradation caused over time by software installs, and the DNS Client service is taking longer because windows is still loading other things in the background.
You could try something like Prio
to permanently increase the priority of this process slightly and see if that helps.