This is not possible. Technically, the map refresh happens all the time. It starts from the north-west corner and finishes with the south-east corner (taking about 5 hours to refresh the whole map), after which it starts over again. So, the time at which each part of the map is refreshed is different (e.g. in Carlin the map would be refreshed at different time than in Thais).
The refresh in certain place may happen only if there are no players nearby, therefore if you keep your lootbag close enough, it won't be wiped. You may also store it safely on a non-refresh square.