We are fixing an issue with long start times in 4.5.4. In the mean time you can do the following to speed up the start...

1. Stop Designer if running. Make sure the underlying Java vm is also stopped(check the same in the task manager that the process is stopped).
2. Navigate to {Designer_install_location}/configuration/org.eclipse.update folder.
3. Create a backup of platform.xml -> platform_bak.xml and open it, perform the following operation on that:
a. Locate <site> tag whose url attribute has value fileackages/eclipse/ .
b. In this <site> tag, remove the list attribute.
For Example:
Initial tag:
<site enabled="true" list="plugins/NOVLBNNRMSYS_2.0.0.20130412105231.jar,plugins/NOVLJDBCSYBB_2.0.0.jar,plugins/NOVLJDBCATRK_1.0.12.jar,plugins/NOVLOFFIOPTL_2.1.0.20130110140328.jar policy="USER-EXCLUDE" updateable="true" url="fileackages/eclipse/">

After change it should look like
<site enabled="true" policy="USER-EXCLUDE" updateable="true" url="fileackages/eclipse/">
c. Save the file
4. Start Designer.