Depending on the agency and the worker and the field, it usually takes “about” a year for a worker to pass from initial expression of interest through application, vetting, fundraising, and on to the field. (Longer, of course, if more pre-field training is required—e.g. college degrees, etc.)
Once on the field, it can take a year or two (or more) to become proficient in the language and culture.
Once a movement strategy is being pioneered, it can take up to or beyond 2 years to reach 4th generation in multiple streams (sometimes far longer—note theological assumption Only God starts movements).
Therefore, all attempts to initiate a movement amongst a new people group or segment should be predicated on a minimum 5-year investment before any fruit is expected, and likely 10 years before fruit/harvests are “very large” (e.g. 10k to 100k).
Anything “shorter” is very probably not going to be sustainable into something “longer”: in other words, you can see fruit in a shorter time (e.g. from a short-term trip, or a quick church planting), but these strategies aren’t multipliable, and don’t see the extended ramp-up that defines an exponential curve, and so won’t be long-term sustainable or reach very large numbers.