Your hidden MMR (ELO-like rating) will plummet below a diamond threshold even while you remain in Diamond. After just a few (~10) games losing against "evenly matched" opponents, you should start playing games where you are considered "favored", and losing them. Eventually you could theoretically be always matched with bronze, even though your publicly visible league does not necessarily need to match your MMR.
However, I have noticed that bnet seems to only stray so far from your league. I could be wrong about that one, but I know a gold-level friend of mine that, after 25 losses in a row, was still being matched with silver and gold players. They could have rules in place that you can't be matched with someone more than 1 league away from your own.
All this is beside the point at the moment. With the current ladder lock, you will not be demoted or promoted no matter how many losses you incur.
tl;dr: You'll have to wait for the placement match in Season 3.
If the Zerg build you are talking about is the Stephano build, or at least close like it, then this answer should help.
What it is
The stephano build as it is called involves the Zerg player fast expanding to 3 bases total when your opponent sees you with a FFE. The object is to get a clear economic advantage over the protoss because it is said that zerg on the same number of bases as the protoss, will lose. Once the zerg reaches about 8 minutes he will have: 3 Bases fully saturated, roach speed reseraching, ling speed researching/done, +1 Range reseraching. By 11-13 minutes, he will have a maxed out 200/200 roach,ling army headed to your front door. He can constantly stream this in during the attack which makes it very effective.
This build is made for ZvP in which the Protoss is doing a Fast Expand build(generally either Forge Fast Expand or YufFE). It is designed to give the Zerg 3 bases very quickly and safely, while avoiding most Gateway timing attacks. -Liquipedia
How I've seen it stopped
I've been stopped as a Zerg player only a handful of times. This is NOT countered by air. Going for air will take time and my roaches will just kill your buildings before your voids could kill the first 10 roaches or lings. Good unit composition and sentries are the key to stopping this build. If you hold the roaches back with good sentry placement you can get almost free shots at roaches not in groups. You can divide the army and destroy it as it comes in while warping in more troops to deal with the threat. He will eventually have to transition if you come up with enough immortals and stalkers with zealots in the front. Since it is super hard to transition out of this build you will have a good window of time to come in and destroy with archons, zealots, immortals, stalkers, and sentries. He will only still have roach while he is trying to get an Brood Lord army. As for the spine crawlers, its not part of the build. He must have added that in but the basis is still the same, focus fire them quickly if you have a huge problem with that.
Sources
Liquidpedia
Day[9] Daily #472
Best Answer
By default it is 15 seconds on hatchery,lair and hive(it stays same).
Depending on gameplay speed:
Note: The queen's "spawn larva" has a 40s cooldown and spawns additional 4 larvae,but the building wont start producing more larvae until the number of them falls under 3 for that building.
Max number of larvae available for one building is 19.