Time to 1000 I would even say more than 25. Around 30-40
Because Showdown town is a minium of 92 races for all Achievements (first in all races for example). That alone are around 3 minutes * 92 races (without loading times) which are 276 minutes (~5hours)
But online takes nearly forever. You need 250.000xp for Lv 30. But the real pain are the 3 voting timers (20 Gametype+5 Track + 20 car seconds?) before each race and the endless loading time. The match self is in the most game types (Knock Out, Trick Rush, Rampage Domination) around 3 minutes.
A bit math.
250.000 XP needed for lv 30. You can get maximum 1000 XP if you score 1. in a full Solo game, 800 if your team wins in a full team game...
This is a minimum of 250 races. I have needed around 700 races despite of around 300 wins because often games are not full and so on. Have one time seen a guy with 420 races who was lv 30, even that are around 20 hours work.
Btw. the boosting trick with "trick rush" donīt work. I have tested it and both teams only got 200 points (we were 8 players) despite of place 1 for both teams..