Hi Debbie,
Assuming you're talking about a three-week cycle, the patient (judging from my OH's experience) feels a bit washed out and low for the first few days (Days 3-5 in particular) and starts to perk up a bit by the end of the first week. But this is just the point at which his immune levels start to fall, and Days 5-10 (or possibly 7-14) are the days when he needs to be extra careful about avoiding infections, and ready to seek urgent help if his temperature goes up. Then by the third week, he's building up to normal again and his immune system is stronger.
So the best time to be away, if you can manage it, is in the week or 10 days before an infusion is due. Glad to hear that Steve is doing well - you're right to make the most of any opportunity to have a holiday.
Marje