When do I put my rain barrel up to start collecting water - The time to start using your rainbarrel is around late March to late April. The most important thing to consider is that the hard freezes in your area are over for the year. Otherwise, the  water in the barrel may freeze and break the barrel.

When do I take my rain barrel down for the winter - This answer depends on where you live. No matter where that is you need to empty the rain barrel before the weather begins to do a hard freeze for the winter months. Usually that is sometime during October unless you live in the extreme Northern climate. Then it may need to be earlier.  Otherwise, the  water in the barrel may freeze and break the barrel.