How long do managed gigabit ethernet switches take to boot up?

Ok here's another data point for you from a PowerConnect 5324. Which is a few generations behind the models you're looking at. So take it for what it's worth.

So the ping command below was sending 1 ping per second to you can see from the output below that it took 108 seconds from the point where it went down from the reload command to the point that it started replying again.

PowerConnect 5324 reboot 108 seconds

date && ping 192.168.0.2 && date
Thu Apr 15 00:06:45 EDT 2010
PING 192.168.0.2 (192.168.0.2) 56(84) bytes of data.
64 bytes from 192.168.0.2: icmp_seq=1 ttl=64 time=2.53 ms
64 bytes from 192.168.0.2: icmp_seq=2 ttl=64 time=2.54 ms
64 bytes from 192.168.0.2: icmp_seq=3 ttl=64 time=2.55 ms
64 bytes from 192.168.0.2: icmp_seq=4 ttl=64 time=2.60 ms
64 bytes from 192.168.0.2: icmp_seq=5 ttl=64 time=2.55 ms
64 bytes from 192.168.0.2: icmp_seq=6 ttl=64 time=2.76 ms
64 bytes from 192.168.0.2: icmp_seq=7 ttl=64 time=2.50 ms
64 bytes from 192.168.0.2: icmp_seq=8 ttl=64 time=2.63 ms
64 bytes from 192.168.0.2: icmp_seq=9 ttl=64 time=3.51 ms
....
64 bytes from 192.168.0.2: icmp_seq=117 ttl=64 time=2026 ms
64 bytes from 192.168.0.2: icmp_seq=118 ttl=64 time=1028 ms
64 bytes from 192.168.0.2: icmp_seq=119 ttl=64 time=30.1 ms
64 bytes from 192.168.0.2: icmp_seq=120 ttl=64 time=3.80 ms
^C
--- 192.168.0.2 ping statistics ---
120 packets transmitted, 13 received, +45 errors, 89% packet loss, time 119202ms
rtt min/avg/max/mdev = 2.502/239.520/2026.970/583.213 ms, pipe 4
Thu Apr 15 00:08:45 EDT 2010

I can't imagine a reason why you would be rebooting switches often enough in any environment to even worry about this. Any reboot of a switch should be done in a maintenance window and then a few minutes isn't going to be a big deal.

I'm not sure how you think that booting time reflects the switch performance. Switches, like most embedded devices, will have an underpowered CPU of some sort which is responsible for the booting process and maybe a few functions such as running the cli or web interface. But almost all of the networking functions are going to be handled by purpose built ASICs and won't involve the CPU at all.

SRW2048 from a cold start running 1.2.1, 97 seconds

tsavo:~ mcd$ date
Mon Apr 12 14:04:48 EDT 2010
tsavo:~ mcd$ ping 192.168.24.70
PING 192.168.24.70 (192.168.24.70): 56 data bytes
Request timeout for icmp_seq 0
Request timeout for icmp_seq 1
Request timeout for icmp_seq 2

... snipped ...

Request timeout for icmp_seq 85
64 bytes from 192.168.24.70: icmp_seq=86 ttl=64 time=45.284 ms
^C

tsavo:~ mcd$ date
Mon Apr 12 14:06:25 EDT 2010

I don't have the exact times on hand, but we have both Cisco (3750) and HP switches (2524 & 2510G). The Cisco ones indeed take several minutes to start up. The HP ones take about 30 seconds. The HP ones are 24 port, and it tests each port (does about 4 ports per second), so a 48 port would take slightly longer.