It can be a difficult time of year for athletes training for a summer Ironman. If it's your first one, chances are that you've put in a lot of time and energy into your training during the winter - and probably even more mental energy into thinking about what you have to do. Now the nights are getting lighter, it's a big temptation to respond to worries and anxieties by fitting in as much training after work as possible, driven by the fear that you're 'not doing enough.' All well and fine if you recover well, but often all that happens is these midweek filler sessions don't do much for fitness, but have a bit impact on your ability to perform well on the weekend long ride.
Reassure yourself - you're consistently training day in, day out, following a well constructed training program (and if you're not, feel free to contact me and I'll write one for you :) ) If you've missed sessions it's for a good reason, like life getting in the way, or colds/illness. We all face this (well, at least working AG triathletes do) and we all give ourselves a hard time. However, reassure yourself - you're doing more that 99.9% of the people out there in the country just by being a triathlete - keep perspective!
Every session you do, no matter how short, is helping prepare you for your ironman. Some weeks you'll not be able to fit in much training, and some days you'll feel physically tired. On those days, if you need to cut a session short, then NO WORRIES. Try to aim for a 20 min minimum at an easy pace, and then pull the pin if you need to. Take a total rest day if necessary. The aim of the week is to make sure that you get your long aerobic bike, your long aerobic run and your long aerobic swim done. Everything else is secondary to these sessions. Still important, and ideally you'll be getting them done, but not at the expense of the big three.