Swamped

If you ignore the fact that you're dealing with time magic, there's a simple answer; retaliate. Send your own disruption back to them. Hopefully it works long enough for you to finish.

But you have another option. Whatever time period this man comes from, this is your one line of communication with them. Which means there's a lot you could learn.

To begin with, you could learn what they want. Then, perhaps, you can use this spell as a cross-temporal negotiation.

But to do that, you'll have to see just what their counterspell does. There are a lot of ways to disrupt a spell, and some are more destructive than others.

So you let it through. Carefully, of course. You control the ether flow so that whatever it does, it doesn't do much of it right away.

And what it does turns out to be simple. It starts to siphon the ether back. Well, that's inconvenient, but it's promising in terms of what it suggests. They're being very direct in countering you, but not putting any effort into doing anything besides countering you. Since there are spells that could do the same more effectively with significantly more collateral damage, they're most likely not trying to start a fight.

Well, then you won't give them one. But you do need to give them a message back. What sort of spell can you use to make your intent as clear as possible, without antagonizing them?