Viernes Culturales takes over the street on the last Friday of every month, roughly 5pm to 10pm, between about SW 13th and SW 22nd avenues. Traffic is closed off, galleries and artist studios open late, there is live music on the pavement and a free guided walk. Nothing costs anything unless you buy it. This is the version of Calle Ocho most worth planning around, and it happens twelve times a year rather than once.
The Calle Ocho Music Festival is a single Sunday in March and is a different scale of event: roughly two dozen blocks closed, dozens of stages, hundreds of thousands of people, and the largest Latin street festival in the country. It is excellent and it is not a stroll. Arrive early, accept that driving and parking near it are hopeless, and use rideshare drop-offs well outside the closure.
The rest of the year, the street is at its best from about four in the afternoon until late evening, when the domino tables are still going, the restaurants fill and the music venues open up. Mornings before eleven are genuinely quiet.
Hurricane season runs 1 June to 30 November, and outdoor programming can be cancelled at short notice from August to October.