Hiya Eleanor!
Welcome to planDisney! Eleanor, if you're excited then I'm excited as a trip to Walt Disney World Resort is one of the best holidays for anyone. We go quite often and always find something new to explore and enjoy. Perfume engraving is something I only learned about this year and I hope to one day also get one for myself!
Il Bel Cristallo located in the Italy Pavilion and
Plume et Palette in the France Pavilion in EPCOT are the locations that engrave perfume bottles. I always take a turn inside the shops to smell all the good things and it is just divine. I now have regrets that I didn't get a bottle engraved as I am a huge fan of J'adore by Dior and engraving is complimentary with the purchase of a perfume! The engraving service for Plume et Palette had their schedule set for Thursday, Friday, and Saturday most weeks as of earlier this year but it could be different now. The engraver tends to be available during busier days such as the weekend. I would time your trip so that you are in EPCOT for a Saturday as that is a common day of the week we tend to see them. I would also speak to the Cast Members in the shop as they have a calendar with the marked dates they will be available.
I don't know the dates and times for the engraver at Il Bel Cristallo as it seems to vary so much that it may not known till the dates are closer. There is a chance that either location may also be able to hold your purchase and ship it if needed. I would ask and this may change but it was true in the past.
I'm so excited that you may have a chance to complete your bucket list item. The shops in all the pavilions in EPCOT have such special treasures and I hope you find even more beautiful things to bring home. Remember to pack them well as they cannot be brought on an airplane as a carry-on. I like to stuff my perfume in my sneakers. It sounds crazy but it works pretty well to secure them, keep them padded, and maybe leave the shoe a bit more pleasantly fragrant.
I hope this helps and you have a lovely time.
Happy Planning!
-Nimmy