Just joined to add a playground zone. I think I did it correctly (Added new nodes where the zone starts/stops and split on new nodes. Set max speed:conditional for times zone is in effect.) but would love if someone more experienced could check and provide feedback. I used ‘Go Map!’ on iPhone and there was no option to request a review on making the commit.
The best way to tag a changeset fpr review is to set the review_requested tag (as an attribute of the changeset). In JOSM there is a checkbox for that.
Your changeset seems OK.
For the speed limit, have in mind that not all data consumers uses or supports the maxspeed tag variants, so you may prefer to tag the default as 30, and 50 in the other times. It’s the same info about speeds and time, but tagged in a way that could be more useful.