The customer needs to accept the delivery, to write a review, and to check "show the delivered work on my review". At the end of this chain, if we write the review as well, it will show as soon as we send it, or after a few days (if we don't). However, if the buyer doesn't write a review or unchecks the portfolio sample option, nothing will be added to our gig portfolio and we are not allowed to share any audio files without permission.
Well, if I didn't receive any updates after I've delivered the files (it depends on different things, could be after a few days or a few hours), I would probably write a follow up to let the buyer know that I'm still available, and that can take all the time needed to review the delivered files. I don't suggest to send a notification just for "having a review".
Tip: we can use YouTube links on our gig pages. If you don't have enough portfolio samples to share directly on Fiverr, select any songs (on YouTube) that showcase your talent and service, even if it's not released by you but it's related to you and to your gigs, and add that link where a potential buyer will see it. This way you've nothing to be worried, you're just sharing it. I've done this through all my gigs, with different YouTube playlists for each macro genre, and I maintain updated the playlists, adding songs as soon as a new release with me on the trombone is released.