I shouldn’t be answering you because I haven’t got X, but you may try something along these lines. Firstly make certain that you are in charge of the display of the dlog by, say, having it appear in a ‘try - on error…’ loop. Then maybe all you need is:
display dialog "Now you see me..." giving up after 1
Unfortunately this does need an osax - Standard Additions. I gather that a few osaxen do work in X. Will this? I’ve no idea - over to you.
Andreas