Means "40 sec" in a row or could i use one booster maybe to get more speed ?

40 seconds in total, not 40 consecutive seconds.

You are free to insert non-offroad parts as long as there is at least 40 seconds of off-road in your map

Exactly, overall the car should be off-roading for at least 40 seconds (basically, the more off-roading, the better), but it doesn't have to be consecutive. This allows you to use any checkpoints and transitions you need to make it work.

Could it be a multilap track?

The amount of randomness will be strong in this month's maps

Ok, I have a map that fits the rules but I won't enter (It's pretty long and I'm still not completely happy with the layout). But it should serve to expose a small flaw in the ruling, even at its current state:
My map is about 4 minutes long and has about a minute of offroad. Quite a bit, even on a map that long, but it's clearly not an offroad-dominant map. But it would fit because the AT would excede 70 seconds (On a perfect run, my time should be around 230 seconds right now) and has over 40 seconds of offroad (61 and some change, to be exact). While this contest is already ongoing, I suggest that on future iterations of this contest you go for percentages - 50% or 40 seconds, the one that's larger, of offroading, for example.

FT»Osaka says:
(...)
My map is about 4 minutes long and has about a minute of offroad. Quite a bit, even on a map that long, but it's clearly not an offroad-dominant map. But it would fit because the AT would excede 70 seconds (On a perfect run, my time should be around 230 seconds right now) and has over 40 seconds of offroad (61 and some change, to be exact). While this contest is already ongoing, I suggest that on future iterations of this contest you go for percentages - 50% or 40 seconds, the one that's larger, of offroading, for example.

Yes and no :-)

1. What we are looking for is innovative off-roading. If you can do that in 50 seconds and need another 3 minutes to "get the car in the right positions", then so be it.
2. A track that is too long is likely going to suffer in the Fun Factor/Replayability field.

I'd rather have entries which are on the border of the topic, than to not have enough entries :-)

But thanks for the input, there's always things to improve.

What about the dirt jumps in Stadium? They are technically a natural surface and fit to the rules of this month's MTC. However, will they be treated the same as the dirt roads in Stadium? If so, there isn't much to work with besides hills. Lots of hills.

I personally would say that they're ok because they do fit the theme as you already said. It's still an offroad map with those.
And I agree, besides the hills there wouldn't be much left over to use.

However, better wait for Alcator's answer, as the amount of restrictions and extra rules, besides the topic, is really high and not too easy to understand

brandonktm11 says:
What about the dirt jumps in Stadium? They are technically a natural surface and fit to the rules of this month's MTC. However, will they be treated the same as the dirt roads in Stadium? If so, there isn't much to work with besides hills. Lots of hills.

yes, the dirt hills in Stadium are OK. They can be used to fulfill the "uphill climb" requirement as well as the drop/jump requirement.