Time2HELP only creates help context numbers for topics that you create manually, and for these topics you can set the help context number by assigning the context number value to the HelpContext attribute. Help context numbers are not created for topics that Time2HELP creates (i.e. topics for classes, properties etc.).
It is not possible to set the help context number using @-tags from the source code, neither from UnitDocs.
Some possible solutions:
Create "manual" topics where you set the help context numbers, and jump to these topics from the application.
Write a map file where you assign context numbers to topic ID's, and include it under the [MAP] section in the .HPJ file along with the map file created by Time2HELP. You have to add your manual map file to the .hpj file and compile the help file from Microsoft Help Workshop after building with Time2HELP, as Time2HELP will remove you manual map file entry from the .hpj on each build.
You can also open you help file on a specific topic from your application using Application.HelpJump (e.g. Application.HelpJump('IDH_Class_Myclass') ).
The name scheme for the TopicID's for the topics generated ty Time2HELP are as follows:
Unit: IDH_Unit_[%Unit.Name%] Interface: IDH_interface_[%interface.Name%] Class: IDH_Class_[%Class.Name%] Routine: IDH_[%Unit.Name%]_[%Routine.Name%] Property: IDH_[%Class.Name%]_[%Property.Name%] Method: IDH_[%Class.Name%]_[%Method.Name%] Event: IDH_[%Class.Name%]_[%Event.Name%]