I am getting download times of 60 t0 90 seconds using the gphoto driver. This is happening with both a Canon 450d and Nikon d5100. Is this normal?

Which image format do you use? When I use raw format (Canon 650D), I get quite long download times to (about 10-15 seconds), but when I use smaller formats it is very fast.

No, it's not normal. I get 5 to 10 seconds download times at most, and for raw formats as well.

It depends on the hardware you are running the gphoto service on. When I use my raspberrypi I see similar download times, when running on my linux Laptop downloading is much faster.

450d has a very low download speed. When I use it under Windows, it takes some time until the image is ready. I'm not sure if it's USB 1.1 or USB 2.0, but the thing is that new cameras are much faster (for example 550d). If you run indi_server in a remote computer, you need to add also the transfer time from the server to the client.

In any case, for astro work it shouldn't be an important problem. For example, if you loose locally 30s, but your exposure is 300s, you're loosing 1/10 of the time. Take in mind that many CCDs are painfully slow, and this isn't usually a problem.