The timezone is relatively the same (+3 hours) so it is not entirely the issue.
But it is an issue. Don't minimize this.
When you start at say (?) 9am in your time zone it's already 12-noon in theirs. They'd be thinking about lunch (and can they take their lunch period whenever they like ?), so for a large chunk of your morning, they can be out at lunch, maybe in drips and drabs, maybe all together.
When they get back from lunch it's also not an uncommon time for teams to schedule meetings, so they'll maybe be locked in a meeting where they specifically won't be allowed to communicate.
But by the time all that's done, you're probably at lunch.
And then they're going home at 5pm (?) and lo-and-behold it's still 2pm where you are.
So time zone is, IMO, a huge issue here.
There is little natural overlap for communication to occur.
Have you considered that if they need something from your office at 9-am their time they have to wait for you or other people in your locale ? It cuts both ways and I suspect you're not factoring in how it looks from their point of view.
I am finding it very difficult to deal with offshore team at my current company. They often don't respond to emails and/or instant messages regarding work-related issues. If they do respond, it takes them several hours for even simple questions which is a lot of time lost.
Time zone overlap again. When you send an email or IM, they're simply not available for quite natural reasons. When they can reply they will either figure it's pointless replying late or they do reply and you're complaining it's late, but from their point of view they replied ASAP.
Management/CEO does nothing about it,
Is this a real problem ?
Does it cause real problems or are you simply irritated by the apparent lack of response ?
I suspect it causes you very few real problems.
so I'm not sure what to do. Does anyone else have this issue ?
As I mentioned above your colleagues "offshore" (from your narrow viewpoint !) are probably equally frustrated by comms from your locale.
Your use of the term "offshore" does seem to indicate a failure to appreciate that they're a perfectly legitimate part of a global business and you need to accommodate them, not just the other way around.
What can I do? Should I really email the CEO about the people not responding?
You adapt to it.
You have raised the issue. But have you suggested a solution other than what is probably the unrealistic one of expecting the other team to be available on demand to match your schedule ?
That's the problem : expectation.
Your CEO doesn't want to hear about your problem, they want to hear about a realistic solution.
From a comment of yours :
nothing is done. Honestly, it's just really frustrating. At this point, I tell them that if I don't receive a response, I will figure it out for myself without getting approval.
If you require their approval for something then you wait for them.
Presuming the authority to override them will simply create a much bigger set of problems, and ones likely to get you fired.
As the devil in in the detail it's very hard to advise you on a specific plan, but a some basic guidelines :
You need to schedule an agreed morning phone meeting with them (as brief as possible !) to discuss issues in your in-box and their in-box that need each other's approval. They, in particular will need this more than you. It may be OK to just have a meeting with one senior person who can speak for them. "Hi Sam, have you anything you need from me urgently ?", than kind of tone.
Again, before they leave at 5pm schedule another brief "anything to do urgently" meeting between you and probably the most senior member of the team out their.
These meetings also create a chance for you to maintain a sense of direct contact between you and foster a sense of connection and team between you all. 15 minutes kept as informal as possible max.
There may be a need on both sides (not just theirs) to arrange for someone with authority to make decisions to be available out-of-hours (i.e. as that applies per locale). Anything absolutely urgent needs to be dealt with through those people. This may entail giving additional payments to some people. It should be used sparingly - it's an emergency, not just I forgot something so I'll annoy Bob now.
Alternatively you may need to get each other and management to agree on devolving authority for urgent decisions to each-other's offices. This can pose issues and I do not recommend it.
You need to keep an eye on that clock - theirs ! You need to start respecting what it means in practical terms.
Just because you send an IM does not mean they're available instantly.
You must remember that none of this is probably their fault - they will have issues with this too. You need to need to find out what their issues are and factor them in - work with them as part of a team to find the solution that works best for all of you.
It would almost certainly be a good idea to have a face-to-face sit down with their team or team leads to get an understanding of your normal schedules and see if any rearrangement (on both sides !) is possible to better facilitate comms. You may both need to plan work around the timezone issue, not just expect something that won't happen naturally.
A very radical suggestion which would be very difficult to implement, and would certainly require money to be spent, might be to see if agreement can be reached to get their work hours to be shifted to properly overlap the main office. Note, that this is very tricky and unlikely to happen.
But above all you have to start thinking of them as team members and peers, not the cause of the problem. The cause of this problem is, IMO, just the clock and a lack of planning by people on all sides.