Malduoni began his preparations only days after the rift opened. It wasn't exactly subtle or hard to notice, that Cheliax was suddenly at war.
It's earlier than he would have chosen to make his move. But not by all that much. His army and his wizards are mostly ready. He can get to work on final arrangements, there.
Of course, it's important to understand first what's really happening over there.
There's another world. One with different magic. Different gods. This is, in some sense, far far bigger than the matter of recapturing Cheliax. And of course it has huge ramifications, for whether an attack on Cheliax is in any way a good idea.
A week after the war begins in earnest, Malduoni successfully gets his first agent past the rift. Cheliax is frustratingly impossible to get people into in important positions, but Cheliax is also mobilizing troops hard and fast. They have very few wizards even at first and second circle who aren't enlisted. However, they do have some retired, honourably discharged wizards, who are now invited to reenlist. And one of them, who was only at second circle when he received his honourable discharge, later contacted the underground church of Iomedae.
Malduoni has been involved in funding that project for a long time. Indirectly, of course, through several layers of cutouts, like he does with anything where gods are involved. But these are strange times, and call for more extreme measures. He's willing to reach out. Not revealing his true identity, of course, but admitting to some of his connection to the underground church of Iomedae, and calling in a favour owed. He's willing to provide more resources to them, now, despite the higher risk; the times warrant it. In exchange, he wants someone to get him across the barrier.
The wizard re-enlists at second circle, despite the fact that, during the interim decade, he's levelled several times to fifth circle. It takes him another week, in total, to fake his capture and presumed-death at Ifteli hands, slip away, and learn that a Dimension Door can get him across the barrier intact. From there he still has to travel overland, speaking to (and mindreading) the locals. Finding the fastest route to the sea. He has Teleport, but not to places he's never seen; the journey has to be accomplished by a mix of Phantom Steed and Fly, depending on terrain.
He knows how to make attuned magic items, for a Plane Shift, and does this - there's plenty of time - but that isn't the primary plan.
...
Malduoni scries his agent every day, briefly. When, another week after the barrier crossing, he finds the man camped beside the ocean - on a remote northern coast, many miles from the nearest village let alone the nearest city - he's ready.
The next day at local-dawn - which Malduoni has mapped out meticulously relative to local time - he's watching. He waits until the man has cast Fly and taken it as far as he can. You can't Plane Shift from a scry.
You can, however, cast Gate from a scry, and Malduoni has it prepared. It's a very conspicuous spell, thus the extra time taken to make sure that nobody will be anywhere nearby to pay attention. If any of the local 'mages', as they call themselves, do notice, there's no particular reason for them to connect it to the war raging in a distant country, hundreds of miles away.
Malduoni parts ways with the agent, after paying the man handsomely in gold and magic items, as agreed. He doesn't know, or need to know, what else the church of Iomedae needs of him.
The war is three weeks old; the rift itself, closer to a month.
Malduoni, alone in a new world, begins his explorations.