Question about this weight loss?

So this is actually multiple questions in one so please bear with me,lol. Ok so not this past Wednesday but the Wednesday before that I started interval training on a stationary bike. (I'm 17, 180 lbs, 5'6, hit my first major plateau about 3 weeks ago so that's why I started interval training ) Sometimes I can not go for very long. Other times I can make it for up to almost 20 minutes of alternating between 1 minute full speed and 1 minute of rest. Question 1: is even just a short amount of time effective? How Long should I do it for at least? Next topic,the past few weeks I haven't been eating super nutritious. But I've still been below my calorie intake( except for like 2 days and even then it was less than 100 calls both days) I'm planning on getting back on track, will this affect me negatively in anyway? For instance today way brothers bday(Mir was LAST Friday, and my friends was on Sunday's and my dads was,well yesterday) so there's been a lot of not super healthy food and today I had a small slice of chocolate fudge cake and also scooped a huge amount of frosting onto my plate)

Anyway I guess I'm just asking between y interval training and my strength training( 4-6 sets of push ups, 25 squats, 10 pull ups) will I break my plateau soon even with my food? (I've still been eating fruits and veggies as well it's just that there's been more junk food as well even tho I eat it in proportion minus the frosting today..lol)

This plateau issue seems to get everybody at some point. I believe the consensus is to spend a couple of weeks or so breaking all your habits. Even if it was / is unintentional you seem to be doing that with eating less for a few days , eating not too good stuff a few. Try eating at maintainance a few days n not exercising a few days. This sort of snaps your body out of a routine it has adjusted into. Best of luck.