Depending on the structure of the trade they can happen at any point now. There are some restrictions on making trades after in league year 2018-19 (players who's contracts expire at the end of the 2018-19 season cannot be traded, for an example) but as long as the trade is legal it can be completed at any time now.
Additionally, the league year rolls over on July 1st (might actually be 6 pm on June 30 this year) so that opens up other avenues for making a trade that wasn't possible at the end of 18/19 now possible in the new league year.