It's not rocket science....
The general election will be on 6 May. GB will want to hold on as long as possible for the economy to improve - he hasn't got a spontaneous bone in his body, and he isn't a gambler. 6 May is the date for council elections in England, so having the general election at the same time saves money. If GB goes on past 6 May he will be criticised heavily in all the press, for wasting money, being scared to go to the electorate, etc, which will all lose votes.....
As for announcing the Armed Forces pay rise.... It is not just the Armed Forces, it is all public sector workers, some 6 million of them, who are all voters. By 20th April (ish) you can check on JPA what your pay for the month will be, and hence your pay rise. Are the government really going to want the press to find out the pay increase from the workforce, rather than announce it themselves.
Any pay rise, or lack of it, will be announced by 1st April at the latest, but quite possibly no earlier!!!