[Calgon]

You can use unix timestamps to calculate it. Once you've calculated, you can use a function in the thread (timec) to convert that to a relative time format.

All you have to do is 60 * 60 * 24 * 30 to calculate how many seconds it'll be in 30 days.

The link for 'unix timestamps' directs to a tutorial which also has an example on how you can do this with extra code.