periodically steps

I try to make periodically steps on workflow. I set WAIT step type and on REQUESTED START set

Refer.date/time : EXP Expression

Date: %DATUM%

Time: %TIMLO%

+ 1 min

but the step have status WAITING all time and dosnt start at ( %DATUM% %TIMLO% + 1 min). It seems that step doesnt create background job