In Flash Video MX Pro, CuePoint helps to achieve this task, now let's see how.
Start the program and import your video in:

Click "Cue Point" to add text to SWF!

a. Play the video, and at the time you want the Cue Point, click "plus" icon, and select "Add Event" or "Navigation" to your video to add text to your Flash.

b. Under "Parameter", please click the "plus" button, and in the "Value", type in what you want to show on your video.

c. Click "Time Offset" to precisely set the "Start time".  OK, click "Next" to continue.

In "Export to", set your destination folder, and keep all others as default. Click "Next" to continue.

Find a Flash Player skin for your Flash, together with the Player Profile, video special effects, and preloader, or just keep the default. Click "Next" to continue.

Click "Start" to begin the conversion. Play the output SWF, and you will see the text effect instantly.