At least EdgeRouter POE boot time depends on amount of traffic very much.
I have offload enabled:
# show ubnt offload
IP offload module : loaded
IPv4
forwarding: enabled
vlan : enabled
pppoe : disabled
gre : enabled
Almost sure the problem is because offload switches on somewhere in the end of booting process after most of the services already up (especially forwarding, nat etc). Thats why router becomes very slow (high cpu usage) during boot.
Please fix it!