You're right, this is Super User category question.
It could be general network contention or fewer users in your country - or your ISP sharing the total bandwidth between you and the server (or more likely, their upstream peers) with too many people. The weakest link in your case will always be the smallest capacity peering link or most heavily contended intercontinental link operated by an upstream provider.
It may simply be that your ISP isn't that great and oversubscribes their network, resulting in you competing with too many customers and their traffic during the daytime.
If they apply Quality of Service to their network to prioritise web, IM and email traffic over game traffic (and perhaps other categories of traffic like torrents and streaming) you may be noticing their network management in effect.
The way to eliminate this as a potential cause is to subscribe to a decent VPN service, connect through that and conduct measurements during the day and night. VPN traffic tends to usually be prioritised as it's very sensitive to latency.
If you traceroute between yourself and the remote server, you can observe the route your traffic is taking (in that instance - which is also probably always the case unless your ISP is aggressively adjusting their routing policies). Use Looking Glass tools and peering database services to figure out whether your traffic is going via an underresourced upstream peer.
In this scenario, using a VPN (who will have their own core network and peering agreements) may negate the problem: you will likely have a good connection to a local(ish) VPN server, and once it's in the VPN operator's private network, their peering links will possibly be better specced (or more lightly loaded!) than your ISP's 'direct' link to the far end.
You may decide that any slight loss of absolute connection speed due to VPN overhead, and any marginal increase to RTT, may be made up for by a more consistent, less laggy connection to your China server.
DNSLytics and similar services return some useful info including ASNs if you want to identify problematic midpoints. Example, looking up info for another IP range:
Once you know the ASN, you can look that up and determine peers. Sometimes a traceroute will even have 'branded' DNS responses for routers in the path, which makes working it out even easier.
There's plenty of sites which will display peering info, BGP routes etc. This is an example of what's available if you search for CloudFlare's Automated System (AS) number to show some info:
You can also find out who owns and operates a router or entire network by using lookup services like DomainTools (e.g., http://whois.sc/8.8.8.8).