Isa help to buy question

[tru.playaz]

Hi, thanks in advance, I have taken out an isa on the basis of using it to buy my 1st property. I understand it has to be open for 12 months before you can access it, all good as was opened a year ago and took advantage of the 25% top up from the government. 

 

My question is how long does the deposit need to be made before I can withdrawal the second year's amount, you are allowed 4000 per year and is topped up to 5000, I understand the 1st year to wait, but is this still the case for the second year's deposit, I.e if I deposit another 4000 and get the 1000 extra, do I have to wait another 12 months to access these funds or are they available sooner, as I will be looking to purchase in the coming months. 

 

I hope this makes sense but cannot find any information, obviously it's a lot of extra money but no good in a year's time.