I created a mod called Unlocks which is basically a copy of the BF2 mod with 64 player maps I downloaded or created. This is the file I edited.
C:\Program Files\EA GAMES\Battlefield 2\mods\Unlocks\Levels\Strike_at_Karkand\Server.zip \gamemodes\sp1\16\gameplayobjects.con
Here I changed the tank spawn to 3 seconds by changing the last two lines. If you want to edit a different vehicle and it doesn't have spawn delay lines then add them.
ObjectTemplate.create ObjectSpawner CPNAME_SK_64_gasstation_HeavyTank_0
ObjectTemplate.activeSafe ObjectSpawner CPNAME_SK_64_gasstation_HeavyTank_0
ObjectTemplate.modifiedByUser FFOLKES
ObjectTemplate.isNotSaveable 1
ObjectTemplate.hasMobilePhysics 0
ObjectTemplate.setObjectTemplate 1 RUTNK_T90
ObjectTemplate.setObjectTemplate 2 USTNK_M1A2
ObjectTemplate.minSpawnDelay 3
ObjectTemplate.maxSpawnDelay 3
Here is a video that shows you the example above:
VIDEO