According to this map:

https://slcairport.com/assets/pdfDoc...-Distances.pdf

The tunnel is 1200 feet long (0.37km), and the longest walk from the terminal entrance to the farthest gate is 3350 feet (1.02km), so your estimate of 1km from Hertz sounds reasonable. According to the map the 3350 foot walk should take about 15 minutes without using any of the moving walkways. I'd routinely cover that distance in about 10 minutes, but I'm a fast walker.