You don’t need to, but it will help.
No matter your speed, having WK organized will save a lot of headaches in the future. That’s what the 12h cycles are all about. Can you do WK without it? Sure, you can. However, if one has problems dealing with WK, having a schedule will definitely help.
Now, you said you could end up getting busy. That’s okay. The problem isn’t with being busy, but with the schedule you chose to do the lessons. If you know you’ll be busy in 4/8h, just don’t do too many new lessons. For some people, skipping these intervals after doing 20 new lessons will be painful and will give them a bad start in those items. Maybe you could just do 5 lessons and you’d be okay because the load wouldn’t be that big.
Now, WK shouldn’t be a bother in your life. If it is, you’re doing it wrong. That’s why having your own schedule is important. The 4h/8h schedule can be done in 2 different times of the day: in the mornings (4h around lunch time and 8h around dinner time) and 4h before your last review (you’ll wake up the following day and do the 8h review).
I’m curious, did you read my big text somewhere around the forums about this topic?