Hey. I just have a few quick cardio questions.
I'm trying to lose some weight and gain some muscle, and Im not sure about certain things regarding cardio; this video by scooby
What is good cardio? made me question my methods.
For a few months now, I've been doing cardio 3-4x a week, jogging on a treadmill (its winter outside, I'll jogg outdoors when spring kicks in

). Then I found out about interval training and for the last month I've been doing that. However I'm not sure if I'm doing it properly.
When jogging in steady tempo for 20min, I chose the speed of ~7,5-8km/h on the machine. Now when doing interval training I run for a min at ~10.5km/h and then walk at 6km/h. Is the running part fast enough? It's not sprinting, just fast running for me. Also should I raise the "walking" part aswell and make it into a slow jogg?
Another thing; when I switched to interval training, I started doing only ~16min of it instead of 20 as I did before with steady pace jogging. I should be doing 20min of interval training aswell right

?
Last question: spring and summer are coming soon and I'm gonna start doing more and more cardio because of nice weather. Im gonna try to do ~40-60min mon/wens/fri and 20min tues/thurs/sat/sun. When doing the 40-60min day, is it ok to split the cardio into 2 or 3 chunks of 20-30min? Or do I have to do it all at once. If the answer is "you have to do it all at once", can I do lets say 20min interval then finish off with a 30min steady pace jogg or does it all have to be either interval or jogging?
Sorry for my english, its not the best but I hope you understood my questions and will be able to answer them.
Thanks

Interval training simply means alternating effort levels. If you mean HIIT (High intensity interval training), you should be working at max effort for 30-60 seconds. Increase the speed of the treadmill progressively until you are at max effort. you should finish pretty well spent.
My steady speed running over a very hilly 5km
averages 11 km/h over the whole distance, and I am 46 and don't really run that much. I usually row or cycle. Therefore I suggest that your "fast" speed is not fast enough for HIIT unless you have a meaningful incline on the treadmill. HIIT involves sprinting for a minute or so, but walking quickly at a 10% grade will work as well. 16 minutes of HIIT is ample cardio for anyone if done right. Some do 30 seconds on with 60-90 seconds slow, some might try 60 seconds high with 60-75 seconds slow for a total of 8-10 intervals. My favourite intervals are a 5 minute warm up with 8 sets of 60 sec high, 75 sec low and a 5 minute cool down for a total of 28 minutes.
Splitting your cardio isn't particularly efficient. You need to warm up each time and cool down for each of the "chunks". You might consider a 10-15 minute steady state warm up followed by 20 minutes of intervals and a 10+ minute cool down if you want 40 minutes. Bear in mind that HIIT will give the same relative benefits as steady state exercise in half the time due to the "afterburner" effect or EPOC (Excess Post exercise Oxygen Consumption) so you really only need about 20-30 minutes rather than a whole hour.
If you are serious about fitness and weight loss, throw in some resistance training a couple days a week as well. For instance, if you have 40-60 minutes 4 times a week, you might want to consider starting with 20 minutes of body weight exercises (pushups, dips, lunges, pull ups, etc) followed by 20 minutes of HIIT. That would be very effective.