I have not seen a response to this question, yet, so you get my 2 cents. If all of your VLANs are single, the only way that they can "see" each other is through a router. If you set the VLAN that your DHCP server is on to be a multiple access VLAN that includes access to the VLAN that your DHCP clients are on you should have no problem. The time out is because the DHCP client waits for a DHCP response from DHCP server for a prescribed period of time, then gives up (times out)- just like a web browser contacting a site that is down or doesn't exist.
Hope this helps,
Southern Kern Unified School District