Okay, so using my sister's sim (24 month Telkom contract) download speeds were fine between 12 and 1am. Switching to my sim (Night Data 100GB) and speeds slowed down significantly.
The test torrent I used maxed at about 800Kib/s on my sister's sim but barely reached 180Kib/s on mine. Then I decided to let it run past 1am and, as expected, the download speed shot up at 1:02am till it stabilized between 750Kib/s and 820Kib/s.
Browsing was also significantly faster from 1am onwards. This pattern repeats itself every day like clockwork on my end. It's really frustrating.
Hoping someone with the same bundle loaded can test this as well...