are you using roaming profile or local profile?
if you are using roaming profile, windows only sync the current user's profile. so the number of profiles on a PC doesn't matter at all.
if you are using local profile, there is nothing to sync.
what matters is the size of the profile (if you are using roaming profile). you can limit the size of profile, or you can redirect some of folders in profile to a file server so it's not downloaded/uploaded when users log on/off.
There are many other factors can affect the logon time, but you didn't provide enough info as you are focusing on wrong area.
if you are using roaming profile, windows only sync the current user's profile. so the number of profiles on a PC doesn't matter at all.
if you are using local profile, there is nothing to sync.
what matters is the size of the profile (if you are using roaming profile). you can limit the size of profile, or you can redirect some of folders in profile to a file server so it's not downloaded/uploaded when users log on/off.
There are many other factors can affect the logon time, but you didn't provide enough info as you are focusing on wrong area.