Dude, what kind of rinky dink operation are you working with that tech support closes at 5PM? It must be some single man WISP because even the small dialup ISP I started with in 1993 had 24x7 phone support. It is likely that the lineman who can fix a physical plant problem has limited hours for residential customers, but troubleshooting and diagnosis that could pinpoint an oversubscribed POP should be available around the clock. The idea that you're going to get a 100% commit rate circuit for $30-50/month is insane. The reality is that for most people ISPs do a fine job of keeping speeds in the usable range damn near 100% of the time, see the FCC 2015 broadband report if you don't believe me. The only consistently bad ISPs are Frontier, Windstream, and Century Link (I had forgotten the third, though there results prior to 2015 were somewhat better). Peak vs offpeak had little impact on the ratio of advertised to achieved bandwidth which means oversubscription was a non-factor.
(as an amusing aside the fiber plant that Frontier bought from Verizon shows significantly better results in the 80/80 test than the plant that Verizon kept, I wonder if they just never updated their advertised speeds or if they're actually managing it better than Verizon)