I need advise on my Nigerian Visa which i received yesterday..?

[Halima]

Hi i received mine and my son's Nigerian Visa's yesterday and im really confused. It says 'Valid for presentation at a Nigerian port within 3 months of date of issue 12th April 2010 if passport remains valid' Does this mean i have to be in and out of Nigeria 3 months from date of issue (12th April) or does it mean i have 2 enter Nigeria within 3 months and then my 3 months starts? im really confused, i am not traveling until end of June but if it means 3 months from date of issue then i have to be home before 12th July..I have tried calling Nigerian Embassy but i can't understand what they are trying to tell me..Can any1 advise me on how my visa works?? Thanks