I'm sure you're thinking of Charles Sheffield's Between the Strokes of Night (1985).
The travelers are a small crew on a spaceship plus their "guests" from a recruiting game that took place on the planet Pentecost. (The hero and his friends were labeled "troublemakers" and shipped out-system.) Space travel takes place at sub-light speeds, but by living in "S-space" where people live at a perceived and metabolic speed of 1/2000 the normal rate, a centuries-long trip will take only a few (experienced) weeks.
The ship's robots aren't fast - they don't even move at a walking pace in normally-experienced time - but to people in S-space they are so fast they're invisible:
But the robots certainly made my life confusing. When I first found myself in S-space I thought I was going mad. Those machines were a big part of the reason. The other people on the ship could make things happen by magic. They asked for something to be done, or they asked to be taken somewhere, and it was accomplished instantly.
Food, besides not being served hot, tastes much different:
Everyone seemed to take it for granted that Peron would now eat and drink the same things as the rest of them. When he arrived there were already five or six different dishes on the table—all of them unfamiliar. He found something that looked like a fish fillet, but clearly wasn't. And there were several pseudo-meat products, each flanked by some kind of vegetable. Nothing tasted quite the way he expected—and all the food was cold.
The others seemed surprised when he mentioned that. Ferranti looked at Garao and at the linguist, Atiyah, then shrugged.
"I should have mentioned that to you before. You won't get hot food in S-space. Better become used to it cold."
There are cabinets that allow people to transition between S-space and N-space (normal space):
Peron was tempted to open the door of the container. Instead, he went to an empty one that stood near to it, and opened that. The internal controls appeared quite simple. There was a three-way dial, a timer with units in days, hours, and hundredths of hours, and a manual switch. The switch setting showed only an N, an S, and a C. The C position was in red, and below it stood a written notice: WARNING: DO NOT USE SETTING FOR COLD (C) WITHOUT SETTING TIMING SWITCH OR WITHOUT ASSISTANCE OF AN EXTERNAL OPERATOR.
In S-space the view outside is completely different:
"Frequency shift," said Sy at once. "Let's see. Two thousand to one. So the wavelengths your eyes could see would be two thousand times as long. Instead of yellow light at half a micrometer, you'd see yellow at a millimeter wavelength. Where would that put us?"
There was a hush.
"The Big Bang," whispered Kallen.
"The three degree cosmic background radiation," said Rosanne. "My Lord. Peron, you were seeing leftover radiation from the beginning of the Universe—actually seeing it directly with your eyes."
Sy uses a later-discovered even-slower time mode to experience the birth of a new universe:
We are close to the end now—mere seconds on my subjective clock.
All outside light has gone. The cocoon is closed. What happens next will be simple, and very sudden.
The curvature of the region that I occupy will exceed critical value.
A new, self-contained region of spacetime will be formed. Its matter content, converted to raw energy, will be that contained within the volume bounded by the contracting Kermel Objects.
And I? It seems to me that I represent that matter content, in its totality.
I, Sy Day, will cease to exist in my present form. I will become a universe.
Let there be light?
Note: most of this answer was cribbed from my previous identification of this book.