Have really focused on my eating and exercise since early December. M weight has gone from 171 to 158.
I am 5 foot 8, 46 years old. My winter Canadian exercise program is as follows:

1) Every other day a 1 hour weight session/exercise ball session. This is the exact same inner core strength workout that I was put through a couple years back when I hired a personal trainer. I am getting cut and have really noticed my inner core strength increasing dramatically. This seems to be working for me.

2) Daily 1 to 1.5 hour ride on my Spincycle. I warm up for 5-10 minutes with light pedalling and than follow a program where I pedal sitting down for 5 minutes with my hear rate in the 130-135 BPM zone and than every 5 minutes I stand up on the pedals and pump a little harder for 1 minute which puts my heart in the 150-155 BPM zone. Than I sit down and pedal for another 5 and keep repeating this for 60-90 minutes.

I am wondering if there is something I can do in this 60-90 minutes that would be better for me conditioning wise. I am only interested in staying fit and lean, my speed on the bike or my ability to race is not something I am interested in at this point. I love to cycle but as you all know, 90 minutes on a spinner is like 4 hours of outside riding. I want to make sure that this time is spent in the most beneficial manner. Should I be varying my hear rate more? Should I be staying closer to the 130 BPM and forget the 150-155 spikes etc.

Exercising at the higher intensites causes many good changes in your fitness like you ability to do other, and more hard training, and helps to raise your BMR. But, getting out of the saddle is silly, and yes, I know every spin class does it this way but you will gain more strength and fitness if you simply increase your effort while in the saddle to raise your HR to the level you want. The reason your HR goes up when you're out of the saddle on your spin bike is because from a mechanical efficiency standpoint, it's terrible. Get out of the saddle just long enough to accelerate and then do the rest of the interval in the saddle.

The hard one minute with 5 minutes rest isn't particularly effective at improving your fitness except in the area of a very high intensity-higher than what you're doing. Better to increase the effort slightly and maintain that for at least 5 minutes, recover for 3-4 minutes, repeat. Choose an intensity that will allow you to do say, 3 of these 5 minute intervals each day you do them, 3 times a week. After about two weeks you could do the intervals for 6 minutes each, or add a fourth interval. Add some time to the total time of your work intervals about every 7-10 days.

Allow for some recovery days because that's when your body actually has a chance to get stronger than before. 3 days a week for your core strengthening is plenty, and 4-5 days a week on the bike will be too. Every four weeks or so just do 2 days of core and 3-5 days on the bike not so hard. You should feel great the following week and that's an indication of appropriate work AND rest.

In another 6 weeks or so you could add a session of about 90 minutes at a slightly higher intensity than your low level.

Train hard. Rest harder.