Hey!
I'm Shaos, I help lead Desolation on Ragnaros, Horde side. You can find our website
here. We cleared LOD+Bane+RS on the old core, and we currently raid 3 25HC's a week, with progress currently as 9/12 (Working on PP currently, havent even attempted Sindra due to bugs recently). We raid at 3:30AM ST, for about 3 hours. Full Disclosure: there are three other worthwhile options to look into on the Ragnaros side, Iridescent, Triumph, and Darkness.
Iridescent's website can be found here
here. They are an Alliance guild that raids at 2:30 AM ST, and currently are at 11/12 ICC25hc. Selaya, who commented above, is an officer in this guild, and can give you more information about it.
Triumph's thread can be found
here. They are also a Horde guild that raids at 1AM server time, and mostly focus on ICC+RS25 normals ATM, though their progress on the old core was 9/12 ICC25hc. We share a lot of members with them, and frequently attend each others raids.
Darkness's website can be found
here. They are a Horde guild that raids at both 20:00 ST and 23:30 ST, and clear old content (Ulduar, Naxx), as well as normal content. They have a bunch of knowledgeable and solid players who've been around the block.
Best of luck choosing a guild if you're looking!