There is a dynamic interplay of factors to take into account, including:
When the first regulations setting carbon budgets will be laid;
The Parliament's scrutiny role in relation to those regulations, and whether the scrutiny process currently set out in the Bill is the right one for them;
The right time after regulations have been approved for the Scottish Government to lay a climate change plan setting out how it proposes to hit the target set out in those regulations, and - counting back from this - the right time to lay a draft climate change plan for Parliamentary consideration;
Whether aligning Scottish carbon budgets with carbon budget cycles set in the rest of the UK should be prioritised;
Whether aligning Scottish carbon budgets with the typical 5-year election cycle of Scottish Parliament elections should instead be prioritised, as well as considering the overall "rhythm" of the Scottish Parliamentary calendar and the impact this can have on scrutiny, especially as an election approaches; and
Overall, the widely-agreed need to get Scotland's climate ambitions back on track as soon as possible and the extent to which that consideration trumps any of the other ones listed above.