You could take that in a multitude of ways.The man takes his scared time getting to business doesnt he?
Is the author (me) drawing this out? And taking his sweet time in writing because he's in the moment? Perhaps.
Is Tristan Schnack nervous? Without a doubt. Is he proceeding cautiously because he is nervous? Yes. Does he know the final outcome of the meeting with Himmler? Yes.
Is it a combination of both the author and the character enjoying the moment? Yes.
Now for the more serious interpretation.
I really think the last few installments take place within one hour tops. It seems a lot longer because Tristan Schnack is recalling these events from various points in time [I haven't exactly narrowed it down to when exactly he is writing, but for the most part it is past tense meaning he survives the war in some form or another].
Tristan's story telling is rather, chaotic at times. He thinks of himself not as a natural writer, but in reality he's very good at the task because to me he is personal as he is speaking from the heart.
As my usual message, stay tuned for the next installments where you guys get to learn the fate of Himmler and a small spoiler! (For those paying attention, notice how many times "Heinrich" was said past few updates? If so, notice who doesn't say it? There is a reason why! Stay tuned!)