Yes, you can join Fantasy World Cup late, during Matchday 1 – for example after Qatar vs Ecuador match. You will get an unlimited budget and you will be changing your team under the Matchday 1 tab as Matchday 2 is locked (so the points scored should count to Matchday 1).
And once you submit your team, you will be awarded two free transfers, so you cannot make unlimited transfers until the end of Matchday! So make sure you are happy about your team before submitting it as after that you do not have unlimited transfers.
And you cannot use your boosters in Matchday 1, as they might be activated only before Matchday start.
Your team’s points should count for MD1, if you bring in UNLOCKED players (those who are yet to play).
And you can join mini-leagues as normal.
Read more: How to play Fantasy World Cup?