We are taking a train from venice to cinque terre mid June and am wondering the best option and how far in advance tickets need to be purchased?
You could buy now and the best practice is to pick the train time that will get you there the fastest with the least amount changes.
What specific town is your hotel in Cinque Terre?
You need the town name when you try to buy the ticket to where you need to get off.
Since the last leg will be on a regional train, unless it is to Monterosso, the schedule is not out yet beyond June 10. In that case you might want to book the Freccia or IC portion now to get the discounted price. Regional train prices never change, so you can wait to buy that.
We will be staying in Manarola. Thanks!
Like Sam above said you could book it now as
Venice to Monterosso to save money and those tickets are in high demand.
That route will go
Venice to Milan
Change trains
Milan to Monterosso
Then at Monterosso (after June 11 or when you get there) you just need to buy a regional train ticket from there to Manarola, which is a 5 minute ride.
I doubt the Venice-Milan bullet and EC trains will or have ever been in high demand to the point of routinely selling out.
The few heavily discounted tickets offered by Trenitalia, on the other hand, will sell out quite quickly. As an example, there are only Economy and Base tickets available on the Venice-Milan trains running next Friday. April 24 is The first day with SuperEconomy tickets left to buy, right before 2 national holydays when most people need to go TO Venice.
The direct Milan-Monterosso IC trains with reserved seats often sell out on summer week-ends, set a reminder on your phone and check again in late May.