Upright Storage

[Catch 22]

My wife's cousin just recently bottled his first batch of homemade wine. For some unknown reason, he used tapered corks (put in the bottle by hand) instead of "real" corks put in by the cute little corking tool, so he pretty much has to keep the bottles stored upright or risk a mess. What is the recommended maximum time frame that bottles should be stored upright? Also, would the same time frame be appropriate for store-bought wine?