Yes I think you are right that the decision to marry may well have been prompted by the knowledge he would soon be recalled to the Colours (ie rejoin the Army for the remainder of his commitment). Since the Munich Crisis in September 1938, the news was all about when, not if, there was likely to be a war with Germany. So he and the other reservists would have known this was coming.
His recall letter was dated 15 Jun 1939, but he was given time to get his affairs sorted out before needing to report to the Depot at Invicta Barracks, Maidstone on 1 September 1939. At that point his commitment was to complete the original 12 year engagement from when he first enlisted on 27 July 1931, but later legislation extended his engagement for 'the duration of hostilities'. The deal was that he was to be given preferential treatment when it came to demobilisation at the end of the war.
Just a couple of other details.
The reference to B120 in red at the top of the page, is to his regimental conduct sheet (Army Form B 120). This would show any disciplinary action against him awarded by his commanding officer, but not any similar disciplinary action by his company commander (recorded on Army From B121 - this would have been retained by his battalion and destroyed once he left the service). The severe reprimand he received later on would have been on his regimental conduct sheet.
The column headed Part II orders on the right hand side refers to the documentation created by his unit concerning various stages of his career, such as postings, promotions etc.
We can see that after his time at the depot where he received his recruit and initial infantry training, he was posted to the 2nd Battalion on 28 February 1932. The battalion was based in Aldershot from 1930 and then moved to Shorncliffe in 1934. This is where he earned his first promotion to Lance Corporal, albeit unpaid at this stage. Since this was just under 6 years after he first joined up, that is a fairly typical timescale for a reasonably good soldier. He was initially unpaid probably as he was on probation in his new rank.
Then on 4 January 1938 he was posted to the 1st Battalion. This probably because he was nearing the end of his initial 7 years of regular service ('with the colours'), and the 2nd Battalion had just departed Shorncliffe to go overseas to Palestine. The 1st Battalion had just returned from many years in India (latterly in Karachi) and were now based in Aldershot.
We then jump forward to his recall to the colours in September 1939. He retained his former rank of Lance Corporal and as we know, rejoined the 1st Battalion. They were part of 10 Infantry Brigade and deployed to France on the outbreak of war as part of the British Expeditionary Force. There then followed the Phoney War in the Autumn of 1939 before the rapid German advance through the Low Countries, and the debacle at Dunkirk, which we have already discussed.
One last item. In the right hand margin are what I take to be his Prudential Building Society Account details. It may well be that he made an allotment from his pay to go to support his wife and this was the account to which the money would have been sent. Otherwise she would have had to visit the barracks in Maidstone every 2 weeks to collect the money in cash.
As a matter of interest who was responsible for the redactions in white at the top of the form, you or the MOD? I was trying work out what information could have been so sensitive as to need redaction by the MOD.