In the original film, a temporal vortex was created when an experiment in 1943 connected with another experiment in 1984; a few things moved from 1943 to 1984, and a few things moved the other direction, while the vortex was open. Now in 1993 when American Mailer attempts to teleport a bomber, he connects with that 1943 experiment, and his spatial transfer works, delivering the plane to Germany on May 3rd, 1943.
At the moment the experiment occurs in 1993, Herdeg shifts to a different world. It is daylight, but by the time he is traveling to Longstreet it is night; they then organize a rather complicated operation and drive some distance to deliver their attack on German Mailer's lab to put Herdeg in the time machine and change history. Herdeg emerges through a portal in the past which, according to German Mailer, will be open for ten minutes. He arrives in Germany at night; the jet is on the ground and Mahler is preparing to launch it. It therefore must be not earlier than May 3rd. Yet upon arrival in Germany, the disoriented bomber pilot will have to find the field and land, the Germans will have to take him prisoner and examine his plane, and will need time to realize what they have, pushing us into May 4th. However, we are told that the past end of the original vortex was open for less than an hour. If German Mailer is tapping the connection to the Philadelphia experiment, he and Herdeg should both arrive on the 3rd, while the vortex is still open in Philadelphia. Once that end closes, there is no connection between the two points in time. By the time they are taking that photo, the vortex in Philadelphia will have closed; no time travel with later arrival times will be possible by that means.
That means German Mailer's machine is creating the opening at the past end as it creates the future end.
This is not the same technology. In the first movie it made some sense for people at different points in time each to open a gate into hyperspace and have them connect, and it makes sense for a similar experiment to open another gate into that same tunnel and send something else through it. Yet for a machine in the future to open a gate in the past is a different concept. You would have to calibrate such a machine somehow for the temporal distance traveled. The original was very much station-to-station, with a power supply at each end to establish the connection, one of which had to remain active to maintain the portal. We have a station at the future end this time; we have no past end station, no second power supply, nothing to target or support the past end.
Of course, this is supposed to be a more advanced technology--more advanced, though, than that used in 1943. Everything else about our Nazi-occupied future suggests that their technology lags, and indeed without the competitive stimuli of the Space Race and the Cold War it is questionable as to whether we would even have invented transistors, let alone microprocessors.
Also complicating matters is that hyperspace seems to be not exactly timeless but temporally very different from normal space. From the perspective of those inside the vortex, the town and the ship are both in the same tunnel "at the same time", even though the one is in the future and the other in the past. We think that the difference in their positions is a matter of their temporal separation, expressed as spatial separation, but we have no notion of how to measure temporal separation, nor even spatial separation, between those points. There is no frame of reference. The probe of the first film enters the vortex, passes the town, then passes the ship. How fast is it moving? How far did it travel? The travel time from the opening of the vortex to the town was not appreciably less than that between the town and the ship--but we would have thought the town to be mere minutes from the opening and the ship forty years beyond it. There is no fixed point for reference. Assuming you could punch a hole into hyperspace and then reach some distance and punch a hole out of it, how would you know how far to go to reach the time you want, and how would you know if you had gone that far?
So the time travel methodology here seems to want us to believe that it makes sense as a new application of what happened in the original movie, but that does not withstand scrutiny. This is different, and considerably less plausible.