How long does it take to build a new team?

The sacking of Paulo Di Canio yesterday, by English Premier League team Sunderland Football Club, got me thinking about how long Head coaches/managers should be given by team/franchise owners before they look to make a change? There are a number of perspectives from which the timing of this sacking can be viewed. In terms of the 2013-14 season Di Canio has been sacked after just 5 games, or 36 days. In total Di Canio had been manager of Sunderland for 4 ½ months and in that t