Great question! What happens is something called gemination, where the consonant is effectively pronounced twice. Some examples from the Wikipedia page:

• "night train" vs. "night rain"
• "unaimed" vs. "unnamed"
• "foreigner" vs. "forerunner"

So in a word like sille, this should ideally be pronounced like "seal lay" rather than "sea lay."

I have always assumed that that was the case. I've always thought that a singular consonant has a shorter emphasis than a double constanant. Or, in other words, you hold the last pronounciations slightly longer.