greenhouse Greenhouse - When to start?

This spring will be my first season starting with a walk in green house.  Previously, had make shift mini green houses but nothing that would build and store the days heat for night.  I am wondering if there is a rule of thumb for how much earlier plants can to into a green house than just into the ground.

Like maybe a X number of days before last frost.  Nothing exact.  Trying to get a handle on how to plan things this year.  Thinking first round of indoor starts gets into green house, second round of indoor starts gets started.  Kind of double what i can do indoors per season.
The culture period is lengthened at the beginning and end of the season for a total of about five weeks.
High tunnel maintains an average difference of 1.5 ° C higher relative to the minimum outside temperature. (32F at night out = +- 34.7)
Must expect a slight difference in temperature between the sides of the greenhouse and the center.
Floricole, well damn that was scientific.  What I am finding at the end of the season is a dramatic lengthening of the season just by escaping the various frost / freeze alerts.  I am seeing near 80 degrees outdoors, there is nothing below 40 in the ten day forcast, but most everything in the field died during two days of cold.  With your information, I am thinking the dramatic extension wont be as dramatic in the spring.

Do you have any knowledge of pit houses?  I understand that at about four feet down you can about guarantee you will not go below 55 degrees if it is properly sealed off.

BTW: I am currently seeing as much as 10 degrees difference in the morning right before the sun comes up.  I think what I have going on is mulch warming the place as it composts.  No clue really, but it does seem more than I should expect.
Jeff H, yep that is what I am thinking.  That high tunnels extend the season mostly at the back end and just a wee bit in the spring.  From what I understand, after about four feet down a partially sunken / underground green house will keep things from ever going below 55 degrees, not the best temp to grow but will keep things alive.

Hawaii, in the current high tunnel are two walkways that are lower than the rows to either side. I am gradually filling them with mulch for the same general idea as the mulch heater you posted.  I dont think it will produce as much heat but it is a whole lot less work.  Figuring the stuff planted in there wont last the whole winter.  So in the spring when I replant, I will use the broken down mulch on the rows.  Might work out well, might not.  Winters arent really horrible here till February ish