Say I apply for a double visa at the embassy - one to use in February and one for April.

If at the end of February, I went up into Laos for a few days, on leaving (overland) would they have to activate my 2nd visa or could I buy a 15 day one (just to go straight to the airport).

Was going to apply but seems like a waste of time (and money) to buy one that would only be used for a few days.

Say I apply for a double visa at the embassy - one to use in February and one for April.

If at the end of February, I went up into Laos for a few days, on leaving (overland) would they have to activate my 2nd visa or could I buy a 15 day one (just to go straight to the airport).

Was going to apply but seems like a waste of time (and money) to buy one that would only be used for a few days.

Sorry I don't really understand your question.

Your second entry would be activated when you returned to Thailand.

If you did not have one you would get 15 days at a land border crossing or 30 days at an airport check point.

If you had a second entry and did not want to use it. The Immigration Officer will sometimes not use this and just give an entry stamp if you ask.

Say I apply for a double visa at the embassy - one to use in February and one for April.

If at the end of February, I went up into Laos for a few days, on leaving (overland) would they have to activate my 2nd visa or could I buy a 15 day one (just to go straight to the airport).

Was going to apply but seems like a waste of time (and money) to buy one that would only be used for a few days.

Two alternatives I can think of:

1. When you return to Thailand from Laos, don't enter a visa number on your arrival card and make a point of telling the immigration officer that you want visa exempt entry and want to save your second tourist visa entry for later.

2. Before leaving Thailand on your way to Laos, get a single re-entry permit for THB 1,000. That will allow you to leave Thailand and return and stay until the end of your initial period of stay (the one from your first tourist visa entry).