I would use it from the very beginning to keep injectors clean. I also like to use an upper lubricant. Redline S-1 does both. Some use it every tank 1 ounce to every ten gallons. Every few months, or every oil change. BG 44K is great to use at oil change. I've used BG44 when I bought my Montero in 1994. I bought it by the case from BG directly through my employer. Never had to have the injector cleans.
It depends on how much money you want to spend and if you're buying Tier 1 fuel. I still use cleaners with Tier 1 fuel. A few months ago I bought Schaeffer's Soy lubricant (upper chamber lubricant) and I like it. After I changed my oil, I noticed a lot of carbon build up in the oil filter. Which means the cleaners are doing their job.
It's a personal decision. Some people don't use any cleaners at all. But, most people aren't OCD BITOG members! lol!
Respectfully,
Pajero!