"The trade must have a reasonable time to mature (and must be reasonably bumped). What is reasonable varies from hat to hat. A good rule of thumb is to go by roughly 25 keys per week. So a trade for a hat <25 keys in value must be up for at least a week. A trade for a hat <50 keys must be up for at least 2 weeks. A trade for a hat <75 keys must be up for at least 3 weeks. For all other hats, the trade must be up for at least a month in order to price them based off the b/o."

This part of the rules refers to B/O drops but I'm fairly certain it applies here, the trade would have to stay open for 2 weeks to make it usable, however, I don't see any reason not to let it mature while this suggestion is open.