foreword: this has absolutely nothing to do with UTC, I don't care what time the server uses.
Problem: events are locked to a specific time of day (ex. 9am-9pm). I believe this is designed for regions like kms/tms/etc that only server one local time zone and thus this covers 'normal playing hours' for all members of that region. We are GLOBAL maplestory though and so 9pm may be the normal time to wake up for some users and they will not be able to participate.
Solution 1: Option one is to allow these types of events to run all day, thus allowing everyone to participate.
Solution 2: Given that a 9am-9pm time frame is about half the day, these types of events could be spread out such that they still are available half the day but are available to more people's specific time zones. Ex. 00:00-3:00, 6:00-9:00, 12:00-15:00, 18:00-21:00.
Some specific events that are limited by this:
Eluna (or so I am told)
2x weekends (but you've already solved this by spreading them out all day, why not do this for the rest?)
GM balloon spawn time for monster collecting event
edit: forgot kritias invasion : )
...and many more future events.