Bombs landing within a fraction of a second is close enough to ‘same time’ for me. YMMV.
While I’m not going to go into specifics for obvious reasons, there is plenty of unused bandwidth in the lasing schema (Information assigend pre-flight to each bomb about the designator.) for a single laser to be used to designate multiple targets.
The actual number is lasing system dependent.
For a Paveway system, as shown in the picture, there are tactical requirements that are also involved in the number of simultanious target which can be hit.