1) Welcome to the Party!
2) when you post, please post your entire configuration including (but not limited to) your installation method and vicidial version with build.
this IS a requirement for posting along with reading the stickies (at the top of each forum) and the manager's manual (available on EFLO.net, both free and paid versions)
You should also post: Asterisk version, telephony hardware (model number is helpful here), cluster information if you have one, and whether any other software is installed in the box. If your installation method is "from scratch" you must post your operating system and should also post the .iso version from which you installed your original operating system. If your installation is "Hosted" list the site name of the host.
If this is a "Cloud" or "Virtual" server, please note the technology involved along with the version of that techology (ie: VMware Server Version 2.0.2). If it is not, merely stating the Motherboard model # and CPU would be helpful.
Similar to This:
Vicibox X.X from .iso | Vicidial X.X.X-XXX Build XXXXXX-XXXX | Asterisk X.X.X | Single Server | No Digium/Sangoma Hardware | No Extra Software After Installation | Intel DG35EC | Core2Quad Q6600
3) Without knowing how you installed your system I will have to assume you have a flawed installation as the problems you present are fairly "freakish".
4) On a side note: Call times are NOT related to the dropping of calls. Call times in a campaign are used to determine which leads are available to the campaign's hopper. Your 6PM call droppage is likely related to UTC being used by your dialer since adding 7 hours to 6PM results in 1AM and there are "processes" that run in Vicidial at 1AM that can hammer the system (and drop calls ...). So setting your clock in the OS (which is OS dependent so I can't tell you how without knowing your OS) and in PHP (which must match the OS timezone or freakish things will occur ...) should resolve your 6PM dropped calls issue.
Happy hunting! Read that manual and look at both Vicibox.com and GoAutoDial.com for installers. Each has its own coolness, but only Vicibox.com's iso is supported by The Vicidial Group (and the entire community of Vicidial Professionals, of course). But many users like the pretty agent interface in GoAuto and CentOS which is a fairly stable OS (as long as you never upgrade ...).