How often should router be restarted

[#1]

Just a general question really.  I have a pretty stable connection, with an Ip profile stable at 5Mbps.  Today noticed browsing was a little laggy, and I noted there was no service status about anything. I was using the RIN network. Speedtests show a consistent 3Mbps rather than the normal 4.8Mbps. I restarted the connection, with no change, and moved back to the Plus Network, still no change. Router had been up for 24days, with a consistent SNR etc, but I did notice a hugh amount of FEC errors, and I mean a high amount.  I completely rebooted the router, and things now appear normal again.  Just wondered why rebooting the router cured things, rather than just restarting the connection to Plus, and how long routers should go between reboots.  I have a speedtouch 585v6, on firmware 6.2.16.3 

[#2]

I am using the same router but with firmware 6.2.17.5 and for some reason my router does a reboot at odd intervals. Other than that I never reboot it and haven't noticed any problems.
However on my Speedtouch 546 with the old DMT tweakable firmware it would occasionally get itself into a mess and start showing up an enormous number of errors. However this was a result of faulty bit swapping and a reboot was sometimes needed to sort it out.
You could try upgrading the firmware which may fix it.

[#3]

Well.... told a little fib,  1 speedtest after the reboot was OK, but the rest are a bit poor, given the IP profile, but browsing appears very speedy, as does streaming on you tube. Odd really.  I am presuming this is down to general contention, on a sunday afternoon, but wonder why speedtests are laggy and show a max of 3.5Mbps, but everything else appears on the surface to be OK. May try RIN again, see if thats any different.

[#4]

I've got a Speedtouch 585v6 running 6.2.17.5 and it has been known to be up in excess of 100 days. (And that was only because there was a power cut then.) My Netgear DG834GT I had before that required a reboot typically once a week because it would get excessively slow or wouldn't connect, etc. Pity the Speedtouch's UI is so poor.
The chances are that your corrected errors and whatnot improve after a reboot because the modem will re-negotiate the sync rate with the exchange and may have settled on a slightly lower sync / higher SNR than before as the time of day may have influenced the SNR threshold.
I've found the router will log FEC errors running to many millions after a long up-time, but so long as they're not regularly happening at thousands per second I don't think it makes much odds.

[#5]

Thanks.  I stuck with 6.2.16.3, as it cured the Idle Timeout Bug, and has been very stable on this firmware, just dosnt work with DMT.  I dont actually think it was a router problem, as it just seemed to right itself, coincidentally after I had cleared the cache, but didnt on my laptop, and sppeds back to normal. Must have been general contention, but not experienced it to that effect before.