Are you mocing IMMEDIATELY? If it is seedlings vs plants over 3 weeks old... there's a bit of difference.
Older plants:
It is preferable to keep your plants in one extended dark period while you are moving them. Do not expose them to dark-light-dark-light. Put them in a bin and only crack it to ventilate every couple hours until you are ready to put the plants back on a REGULAR, TIMED light cycle.
Seedlings:
A rubbermaid bin with a couple of those tube-flourescent camping lights in it is an okay temporary home. Duct-tape the lights SECURELY to the inside of the bin lid. Your seedlings may very well stretch during that time, but they may be re-buried right up to the cotyledons when you are ready to transplant them.