This is from a couple of weeks ago by Alex Massie, I think it covers the issue that this is not what might have been the chosen timing well. I do wonder if there might be a hope in a few very senior SNP people that the UK govt does refuse to allow the referendum on the proposed timescales, and that in doing so allows a Take Back Control narrative to be used.
https://www.spectator.co.uk/2017/03/scottish-independence-looks-riskier-than-ever-but-dont-bet-against-it/
I think that would be how any stalling tactics by a Tory government would be portrayed here: on one hand this would intensify the feelings of those who are already pro-independence, and perhaps May et al hope that dragging things out will eventually see even enthusiasts for independence worn down by the delay, but it comes with the risk that as the insanity of Brexit unfolds it might make independence more attractive to those who are currently undecided or against.
That Brexit has been instrumental in indyref2 is undeniable, since it is the 'material change of circumstances' grounds, but the oft-repeated 'will of the British people' argument we hear from unionists seem to be rarely accompanied by a recognition that the 'will of the people' in Scotland and NI was opposition to Brexit but even so I think it would be a mistake though to see indyref2 as just being a response to Brexit.
Looking at the Westminster general election results from 1970 onward show the maximum number of SNP MPs prior to 2015 was 11 in the second 1974 election, which went down to 2 in 1979 and remained at 2 in 1983, and thereafter was 3 (in 1987 and 1992), 6 in 1999, 5 in 2001, 6 again in 2005 and 2015 - but then 56 in 2015, which reduced the three main unionist parties with one seat each. The situation regarding Westminster since 2015 is therefore fundamentally different - prior to 2015 the bulk of Scottish MPs were from unionist parties that were either part of the government party or part of the main opposition party and, therefore, there was some shared commonality with political representation in rUK, but with the implosion of Labour everywhere and with the Lib-Dems being sent to the naughty step (for now anyway), highlights what is glaringly obvious: that the political makeup of Westminster no longer reflects the political makeup of Scotland.
So, it now seems likely that for as long as Scotland remains part of the UK it cannot feel represented by what may be a permanent Tory government in Westminster (given the demise of Labour everywhere) that has just one seat here in Scotland and was daft enough to let Brexit happen in the farcical way it did for party reasons, and where despite their attempts to portray Brexit as being an elegant purse it is clearly a sow's ear.