Two years would be sufficient to build confidence and then ask for a mandate, wouldn't it?
Calling an election in the face of opposition obstructionism could work, but opportunism will be picked up by the electorate and it will punish, as the Peterson government in Ontario found out to its dismay in 1990 when it called a general election three years into its mandate.
The electorate surprised everyone (including the winners) when the NDP wound up as the government. The NDP had until then been seen to be a perpetual third party. It was a protest vote run amok.
I recall Peterson's remark half way into the campaign: "The voters are cranky".
Agreed that a minority government is a different case, but if it is seen to be able to keep the confidence of the House the conservatives might be better to continue to do so.
OTOH a novel issue can be a justification for an election. If a government decides on a course of action that had not been in contemplation at the time of the last general election. A government can legitimately seek a mandate for that course of action and if it is truly novel, the electors would respect the election call.