lots of misinformation in this thread
please allow me to concur to you exactly all the daily/weekly sources of tokens
60 tokens from ads per day, not 50. it's 1 ad that you have to watch on mobile or puffin browser, then the remaining 29 ads you watch on pc, restarting the client every time you finish watching one
increasing token rewards from the daily login advent calendar on average ~12 tokens per week (I forget exactly how much each gives)
you can get anywhere from 15 (if you're really bad) to 100-150 tokens from raid weekly (if you're better than average), even the regular noob should be getting ~35 tokens from the raid every week. also you get like ~25 tokens from just completing each tier of the raid, however this still assumes you can even complete all the tiers, which most players can't
10 and then 50 tokens from weekly clan arena win contributions, totaling to 60 (I'm pretty sure there's an even higher token reward after, but nearly no clans today are dedicated enough to accumulate 3000(?) wins per week, since it would mean 125 wins from every member of a full clan, especially during 3v3 season
finishing 4 daily quests gives 10 tokens
there are also special quest events which range from ~100 tokens to ~200 tokens, however these are few and far between so you shouldn't rely on them entirely
same as the point above goes for portals, everything about them is almost entirely dependent on the goodwill of the developers. sometimes they are the overbuffed guaranteed premium item and 200 token reward portals, sometimes they're the crappy "gold" portals, which are obscenely easy to complete and give less gold than the average grind mission a regular player already does
achievements, the hard ones give like over 40 tokens each (not worth it in my opinion, since some of them take more than that in respawns to complete)
and the both most and least reliable source of tokens in the game is:
it's very easy to accumulate many hundred of tokens at the beginning of the game by steamrolling through the campaign, but later on, you'll reach many hard stops, where you'll need to upgrade your mechs for quite a while before attempting the missions again. not to mention that both the achievements and the campaign are a finite source of tokens, as in, you'll reach a point where you will be physically unable to receive any more tokens from said sources
in the end this makes it so most players can easily make at least 90 tokens per day/~630 per week
so to answer your question, it takes at least a month to get 4000 tokens if you make use of all the sources mentioned here