training question HIM

If you're asking about the necessity of two a day workouts in half ironman training, my opinion is that they are not completely necessary for success. The key is really maximizing your training time. If you can't fit in multiple workouts "big" in one day you need to make sure you're getting the most "bang for your buck", a lot can be accomplished in 25-30 minutes of swimming or running. Maybe you can restructure some of your workouts to shorter but more effective sessions that will allow for "sneaking in" a second session.

Can you do the workouts back to back, or with a short recovery period between? If you are home early afternoon it seems like there might be time to get in two workouts. Normally with two a days, they won't both have high volume/intensity. I would do the more challenging workout first, and the less challenging one later. An exception might be swimming if you are a fairly beginning swimmer--technique tends to be better when you're less fatigued. In particular, I'd avoid run speed work after a hard swim or bike workout, unless the plan specifies that it's a race simulation--the potential for injury is pretty high if you're running hard when fatigued.

When I'm doing doubles during the school year (teacher), I typically do one workout (trainer or run) before work, and one (usually swim) after work. But at home in the summer, due to different weather conditions and pool hours, it's pretty common for me to run or ride the trainer around 8 or 9 AM, and swim between 11 and noon, or swim at that time, and then do a run or trainer ride later in the day. It works fine as long as you stay hydrated and refuel adequately after the first workout.

It has more to do with the morning/evening.

Currently I do a run in the afternoon and a swim immediately following or a bike ride in the afternoon then a swim following. they seem to be fine. Should I think about switching them around?

I also do bike+run, but very light running.

I'm also signed up to do the Long Beach combo race in Oct, so I want to be prepared for that. it's a 20bike+half Marathon

Unless you are a really strong swimmer (and even then, maybe for one workout) if logistics are just as doable, you might want to think about putting one or both of the swims first. I know for me it can get to be a problem since I'm almost always swimming when fatigued to some extent from a earlier workout and/or a long day at work. In my case I don't have any choice as I don't have AM pool access during the work week, and long runs/rides have to start really early (as in first light) on weekends due to the heat. I feel like sometimes my form gets sloppy due to fatigue; occasionally I have to use a pull buoy or fins to finish a longer workout if I'm really tired from a hard run earlier. I know I'm much faster and smoother when I haven't done a workout before the swim, particularly before work.