I think you should put
let g:Tex_FoldedSections = 'labday,experiment,subexperiment'`
in your .vimrc
itself. If you take a look at ftplugin/latex-suite/folding.vim
you'll find:
if g:Tex_FoldedSections != ''
call Tex_FoldSections(g:Tex_FoldedSections,
\ '^\s*\\frontmatter\|^\s*\\mainmatter\|^\s*\\backmatter\|'
\. '^\s*\\begin{thebibliography\|>>>\|^\s*\\endinput\|'
\. '^\s*\\begin{slide\|^\s*\\end{document')
endif
Which means that setting Tex_FoldedSections
after the plugin as already loaded will not work. Also make sure that your sections in your latex file itself are nested correctly.