Actually, it seems like PHB is the source governing use of SLAs with respect to PCs, while the MM covers SLA usage for npcs.
So for a PC, using a SLA is a standard action or its original casting time, whichever is longer.
No it is not.
See my quote from PHB
"A spell-like ability has a casting time of 1 standard action unless noted otherwise in the ability or spell description."
Add to that the Rules Compendium (which addresses spells with casting times of less than a standard action).
The rule appears to be:
It is a standard action unless specified otherwiswe in either the SLA description or the spell description.
Rules Compendium trumps earlier sources but that does not mean it addresses everything, in this case it addresses spells with a casting time of less than 1 standard action.