Are you dealing with actuall potting mix or the peat pellets that you have to wet up in order to get them to expand to their full size? if you are just putting them into regular potting mix that is dry you may have a problem wetting the soil up and not disturbing your seeds at the same time. IF you are using the pellets you have to wet them up first. If you are only talking about a weeks worth of time I would just start my seeds in the whatever pots water and all and if you are lucky they will just beginning to germinate by the time you are ready to plant in your greenhouse. I start a lot of seeds under flourescent lights in my house before the weather warms enough to put them into my unheated greenhouse. Do take care that you protect your little seedling in the cold night temperatures.