Thats Max duration of record time ie 4-8 seconds max. You will have to download the actual datasheet for each of the devices you are considering to see if that devices capabilities meet what you actually want it to do.
From your description you need a device like the outdated ISD2500, one that has a simple 'push button' addressing mode, multiple message playback etc. Id check if those DIE chip on board devices that you list have all these capabilities first.
The ISD devices are constructed of cells (varying in size depending on device). Each recorded sound uses X number of cells so for each sound there is a little wastage but not alot.