You have to keep in mind that this value is an accumulation since the last server restart, so if your server has been up for months a wait time in the millions isn't that much. I've got a server that's been up since December and the WRITELOG wait is over 6 million but that is only about 0.06% of the time the server has been up. You'd be better off looking at the % of total waits that WRITELOG is using.

Also a reasonable number for your system may not be a reasonable number for someone else's. You need a baseline and then you can find what is not reasonable (normal). If my logs are on SSD's and your's are on 7500RPM spinning disks, your number is not what I should be getting.