There's no specific 'continuous residence' rule for ILR as a spouse - you don't have to stay in the country for a particular number of days.
All you have to be able to show is that you and your spouse have lived TOGETHER, at the same address as each other, and have been in a genuine relationship for the entire 5 years. You do this by showing evidence of mail addressed to both of you at the same address, evenly spaced (every 4 months or so), over the entire 5 years (so start saving your mail when you arrive in the UK).
If you have to travel for work reasons, this shouldn't affect ILR, as long as you continue to keep your joint residence as your primary home - as this kind of travel can't be helped. Even if you both move to another country for a few months during the spousal visa/FLR(M), this may not affect ILR either, as long as the UK continues to be your main residence and you both continued to live together during that time.
But if you choose you live apart for personal reasons (i.e. one of you lives in London and the other lives in Manchester for no other reason than you don't want to live together), then they may not believe you are in a subsisting relationship and so can refuse the ILR.
There is a restriction on being outside the UK when you apply for citizenship - you cannot have been outside the UK for more than 270 days in the previous 3 years before applying, with no more than 90 days in the final 12 months.