I would say up to a year depending on the school and what they have on their list.
My 2018 got his first D1 offer and a couple of D2 in fall of 2016 but had mentally said he would commit around his 18th birthday, in September of 2017. Those coaches stayed in touch over the winter, just occasionally calling or emailing to check in.
Once his junior season started (we play summer ball) contact picked up. Some was initiated by son, who had a list of about 12 coaches that he texted IMMEDIATELY after each game with a basic update (this is an example of what he might send):
Hi, I pitched tonight vs. ??? Threw 72 pitches in 7 innings, struck out 8 and walked 1. My curve ball was really working well. One of my teammates had a home run to help us to a 6-5 win. It was a great team win. Hope things are good with you, hope to talk soon.
One coach came to Iowa from 16-hour drive away and spent a few weeks here going to a lot of games, including my son's. He called weekly. Not sure what they found to talk about, but they did.
The school son ended up choosing reached out his sophomore year and invited him to a camp, then we didn't hear much from them. But during his junior year, we saw the HC, PC and RC all at different games and he started getting an occasional text or letter from various coaches. They invited him to another camp this fall, and made an offer after he pitched two innings.
Most schools asked if he had offers. He usually answered honestly, including when they asked who had offered. Quite honestly, there were usually multiple college coaches at the games and they kind of felt like little reunions — I once mistook a covey of college coaches gossiping behind home plate for a bunch of dads from the other team.