T5 florescent bulbs work very well with seedlings.
The HID produces more heat which could adversely impact your your plants, thus I suggest save the electricity and use the T5's only for the first few weeks
Dr. Jekyll
Maybe you should run them all to determine if you can fry your seedling.
MH is typically used during veg mode, and HPS for flower
You may wish to consider using the T5's as additional supplement for both veg & flower, as your 250 watt HID is not what you would call overkill.
Mr. Hyde