If I understood your question correctly it is no, If you for example take the fonts Arial, Helvetia and sans-sarif the visitors browser look for the Arial font and if the user have that font not installed on his computer it takes the Helvetia font etc..
now, say that I select each of these and set the font to being "Arial, Helvetica, sans-serif". When you look at the HTML code it will say that each of these has face="Arial..." because I've set each of these fonts and this piece of face code will be repeated, will all of these "face" lines have to be interpreted by the browser before it shows the page, and will this slow down the loading time?
It will slow download time as much as you added extra bytes to the file downloading.
If you had <font face="arial, helvetica, sans-serif"> which is 42 characters ten times your adding 420 bytes to the file.
If the lines are contiguous you can add it once. If your changing the font face on multiple pages you can put it in a linked style sheet give it a class name and refer to that in every line with "class=blah" which is much less than 42 characters.
As for how fast the page is rendered on the page the code shouldn't have an effect. Installed fonts are saved to the Registry or the Mac's equivalent (forget what it is called) in a database format so finding a font is fast. Its not like the system has to load each file and "ask are you arial?" until it finds the right one.
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