The Bitcoin transactions are stored in a node's memory pool for 72 hours by default, though some nodes are configured to keep mempool transaction indefinitely. In any case, a transaction will simply return to the mempool if it is still being broadcast (as transactions usually are until they are confirmed). Normally it takes you around 2-3 days what I saw in past and had on my own.
RE: Bitcoin unconfirmed transactions. Is it network overload?