wait workflows ordering

Hi Experts,
I have few questions regarding wait workflows. From my personal learning i found that if i put a workflow which waits for 30 mins below another workflow which waits for 30 days, the 30 mins workflow doenst simply work. Is there any thumb rule to be followed while ordering workflows?

Also there are few wait workflows in our system which waits for a specfic time period expression ( a direct date value is given in the expression which can be dynamic). So if i put my 30 days wait workflow below this will it work?

Please share your ideas on this.

Thanks