In 30 mins you can do a pretty decent strength training workout IMO (once youve gotten accustomed to it). You can easily hit one body part (chest/shoulder/bicep/back/legs/etc) in this time, if not two.

Not when you get to heavier weights and spending 5mins+ rest periods between sets. To be clear - I'm talking about compound movements like squats, presses, deadlifts. If you're just doing bicep curls or something use a rest-pause DogCrapp-style training and have at it.

Ouch. Try classic bodyweight training (e.g. Mark Lauren's programs, they generally fit into this time frame) three or four times a week. Not to mention tabatas. Those 4 minutes can get very long...

30 mins a day is fine. You have to use split training instead of doing a full session with a rest day in between. That’s less beginner friendly but that’s not a big issue.