What's your streamyx package/speed?

You need at least 1Mb for smooth SD videos & 4Mbit for HD videos.

Mostly evening time 6.00pm~12.00am traffic jam.

You can try switch off you router's wifi RF carrier & use direct LAN connection, if your speed recover then you have:
a) wifi theft - change your wifi security passkey with WPA/WPA2 setting.
or
b) poor wifi range - reduce your PC's distance.

TM's "Best effort" service is at least 80% of the subscribed speed, you should get at least 819Kb.

Here's what you should check:
a) any big event/change since last month's OK condition?
e.g. phone line work, modem setting/location/splitter, lightning strike, wind storm etc...

b) post your modem's status here during slow condition.
e.g. [attachmentid=3127593]

c) connect modem/router directly without splitter & do speed test using TM's speedometer
http://58.27.105.110/index2.php?1713166049

d) post your modem's status here again after c).

What's your modem's brand & model?

OK, to see your modem's status, here goes:
a) Start web browser and type 192.168.1.1 in the URL field & press Enter.
b) Enter default User Name admin and default Password admin & click OK.
c) At main menu click Status & sub menu click Device Info.
d) Copy all info from ADSL section & post it here.
    ...you can copy paste as text or print screen as picture.