Firstly, this is 30 cumulative seconds within a round, not consecutive.
Now, I found this achievement quite tricky in a crowded lobby. If you have 3 or more people in the game, your going to struggle as you will have so many people knocking you off course.
I think I won around 15 games or so before getting to 100. Being just in one trail will cause your score to increase, but obviously reduce time left in the round towards the achievement.
There are two "main ways" to obtain the achievement :
a) be lucky and get into a lobby with only 2 players, then just try your best to win.
b) I won this achievement in a full lobby of 6 players (which I could scarecely believe). The tactic was this : Don't attempt it until around level 22-24. Most people in this lobby are level 1-8, with no ability upgrades or weapons.
By level 24 I had unlocked the Lambo Murceliago. It has full speed and nearly full strength. My tactic was to use spawn (level 14 required) and spawn behind the trail car. I then sat behind the car in the lambo. Now, the lambo is that strong that none of the other 5 players could knock me out of the way. Trust me, if your struggling with this, wait for this car. It's super fast, and if you do get knocked off it will overtake anything in front of you.
It's the best way I can recomend, as I was trying from level 10 onwards and despite winning lots of games, I didnt come close to the 30 seconds. Wait for the lambo, its nearly unmoveable. Once you get behind, its then very hard for anyone to knock you off (and most players in this lobby wont have impulse yet).