Hi,
I haven't found alternate way to set the combo value but I have found the solution.
There is an advanced runtime option "Replay using running SAPlogon application". When not set, LR launches SAPlogon application. And then when the Choose time dialog is opened, combos are not filled with all values (yet, or in this mode LR blocks application's UI event message loop or whatever??) and therefore sapgui_select_combobox_entry fails.
However when set the runtime option and I launch SAPlogon by myself, replay works just fine.
Thanks,
Ales