Quebec in Canada is very different to Scotland in the UK, but there are some parallels. Those advocating independence in Quebec lost a referendum in 1980 (60%-40%) then again in 1995 (50.5% to 45.5%). Since then there has not been another referendum on the matter.
Furthermore, in the most recent Canadian federal election (2011) Bloc Quebecois, the federal party advocating Quebec independence lost almost all their seats. If there’s another Scottish referendum this is not the way the SNP will want to go. For Nicola Sturgeon, timing will be everything.
The 2016 manifesto will be an interesting one. Many of the new members joined on the back of the independence referendum defeat so might be expecting another promise, but 2016 might be too soon. Furthermore, with Nicola Sturgeon repeatedly saying that 2015 was not about independence, it shows that she can appear to be distancing the party (albeit temporarily) from one of their core reasons for existing.
Sturgeon has talked about another referendum when circumstances change, for example if the UK votes to leave the EU, but if Scotland votes to stay. It’s a good tactic, allowing her party to remain focused on independence, but does not make them look as if they are rushing it. It's an interesting political balancing act.
Unless something big changes the SNP will win the 2016 Scottish elections with a majority, or perhaps a minority and helped by the Scottish Greens. For this parliament it will likely suit the SNP to only promise a referendum if something big changes.
However, in 2016 the SNP will likely face a choice about the election following it. Scottish elections are held every four years, but when the UK government implemented the Fixed Term Parliament Act that meant that the UK and Scottish elections were to be held on the same day in 2015. As a result the Scottish Parliament was allowed to vote on changing the date to either 2014 or 2016 - and it chose 2016. With the next two elections set to clash in 2020 this will likely happen again, resulting in the Scottish parliament being faced with a choice of a 2019 or a 2021 election.
Resultantly, this will lead to the SNP (if they win said election) having a say when they want to hold the next referendum. 2019 might be a good choice for the next election as the SNP will likely be riding on their 2015/2016 success.. Furthermore, it would be four years into a Conservative majority, something that could play into the SNP’s hands. However, 2021 could also be a good option, as it would give the SNP another five years to show the country its potential success with Holyrood’s new powers. Then again it could give Labour enough time to build up support and beat the party.
Sturgeon and her party are playing a risky game. Two failed referendums would likely not end well for the party. Sturgeon is playing the long game, but I reckon that a 2019 election, with a referendum after the UK general election in 2020 (assuming the SNP win in 2019) would be the best option for the party and its end goals. And with independence just a five percentage point swing away, I reckon the urge to go for it again so soon will outweigh the desire for a long game.
And just for your information, here’s another interesting parallel with Canada. In 2008 the Conservative party fell short of an overall majority and formed a minority government. In 2011 the Conservatives called an election and ended up with a majority. In the UK the Conservatives formed a coalition rather than a minority administration, but like in Canada they went on to to get a majority.