Doing a quick search you'll find other people complaining about some default Safari timeout issue. It seems Safari has something around 10 ~ 15 seconds set for XHR (ajax) as time out by default and the only way to overwrite it is in the javascript code. Also, there's some controversy here, some says that you can overwrite it in the javascript ajax call, others say that Safari simply ignore it. Please, see:
What you can do is to file a ticket for Sitecore support and ask them if they can provide you some patch to work this around.
Also, you should check how your content tree is structured. Slow loading means you have way too much direct child items in a node. You might want to split it between multiple folders or perhaphs use Bucket.
e.g.
/Sitecore
/Content
/Site
/Home
/Components
/Component 1
/Component 2
...
/Component 150
/Component n
You might want to reestructure it as
/Sitecore
/Content
/Site
/Home
/Components
/Group Component A
/Component 1
/Component 2
/Component 3
/Group Component B
/Component 1
/Component 2
/Component 3
...
/Group Component c
/Component 150
/Component n
Adittionaly, you can use prefetch cache for items in the master
database, which will make the item loading process faster. However, be careful when playing with prefetch cache as it can slow your application start. I suggest you reading my blog post on How to patch Sitecore Database Prefetch Caches. You find also other useful resources about this topic such as Friday Sitecore Best Practice: Configure Prefetch Cache and a vast material in the Sitecore documentation.