Training in a new pool

I never have enough time to train. So my workouts are light by most standards. On a regular basis I can fit in 35-40 min with maybe an hour long swim once a month. Generally I'm doing 1500 to 2000 per work out maybe three times a week in a 20 yard Y pool. Always really early in the morning. Two weeks ago I found a place to swim during lunch. The great thing is the pool in 25 yards, the bad thing is I can only swim for 25 min. I'm finding though that the 1000 yards at lunch is alot tougher to get through than the 1500 in the morning, doing intervals at both workouts. Must be the push-off from the wall turns in the smaller pool that make it feel easier, I'm lifting weights in the morning before the lunch swims too, so I'm feeling that. Anybody know any benifits or drawbacks to swimming short workouts, maybe even two a days ? I'm not doing them now but I may over the winter. I'd really like to do some longer (for me ) Open Water swims next summer. 1 mile plus.