Time Based Bandwidth Control

That sounds like a job for PCMM - it's the only way I know of to dynamically change service flow speeds without rebooting modems.

if you use Cisco CMTSes you can use

Cable QOS enforce rules

cable service class 3 name D_HS4
cable service class 3 downstream
cable service class 3 max-rate 5200000
cable service class 3 max-burst 3044
cable service class 3 min-rate 0
cable service class 3 min-packet-size 0
cable service class 3 max-latency 0
cable service class 3 admission-timeout 200
cable service class 3 activity-timeout 0
cable service class 3 priority 1
cable service class 5 name D_HS3
cable service class 5 downstream
cable service class 5 max-rate 3200000
cable service class 5 max-burst 3044
cable service class 5 min-rate 0
cable service class 5 min-packet-size 0
cable service class 5 max-latency 0
cable service class 5 admission-timeout 200
cable service class 5 activity-timeout 0
cable service class 5 priority 1

cable qos enforce-rule D11_HS4
monitoring-basics peak-offpeak docsis11
penalty-period 120
service-class registered D_HS4
service-class enforced D_HS3
peak-time1 17 d 120 avg 3200 peak-time2 19 d 120 avg 3200 d 240 avg 3200 sa 15 do enf
enabled

The way it works is the cmts uses a sliding window to determine if a user is exceeding the rule, if so it applies a penalty service class for the penalty duration.

In This example the qos profile in question is HS4 normally 5.2 megs, peak time 1 is from 5pm-7pm and peak time 2 is from 7-9 pm. During these peak times there is a sliding 10 min window, if the modem in question averages 3.2 megs for the duration the service flow is changed to D_HS3 which tops out at 3.2 megs after the penalty time has expired the modems service class returns to its original service class.

This requires you to set the service class name in the modem config for this to work.