I had thought about writing a shell script to do something similar, for me this would involve 3 steps:
1. learn to write shell scripts.
2. Write script.
3. Enjoy!
Still stuck on step 1.
Anyway the basic job is fairly simple, some pseudo code.
Code:
Run at 4 pm (for evening stm)
10 start_total_data = snmpget -v 2c -c public 192.168.100.1 IF-MIB::ifOutOctets.1
20 Wait a bit
25 if time> 9pm then stop
30 Data_Since_STM_Start =(snmpget -v 2c -c public 192.168.100.1 IF-MIB::ifInOctets.1) - start_total_data
40 if Data_Since_STM_Start>(some amount dependant on package and when you want warned) then Do_something_to_alert_user else goto 20
Unless of course SNMP is disabled on you modem, though you could run it on your router if it supports it.