Is it posible to make a batch smart campaign that can sync lead from SFDC to marketo like every “n” hours 500 lead will be updated.
The global sync process will automatically sync any lead changes without any action needed on your part. The "Sync Lead to SFDC" Flow step is only for pushing leads for the first time from Marketo to SFDC.
To clarify this, Steve is right, but keep in mind that the batch sync will push over any leads that qualify for the smart list you use.
There is no way to say "every 5 hours, sync 500 leads". It's more like:
Every day, sync the group of leads that match this smart list.