No, Trump can’t legally postpone or give reprieve to TikTok. The time has passed for that.

Once Congress has enacted a statute and the President has signed it into law, the executive branch must enforce it. An executive order cannot override or suspend a duly passed law unless Congress included an explicit waiver or suspension provision in that law. Nothing in the text of this act appears to grant the President such discretion, so there is no straightforward way for the President to “undo” or pause the ban by executive order. The only way to alter or lift the ban would be through new legislation or a valid constitutional challenge in court.

That seems unlikely considering the Supreme Court already rules on the matter.