If you notice that your Steam connection only has issues during certain hours of the day (usually in the evenings between 5pm and 11pm), it is probable that your ISP is blocking or "shaping" your connection. Please test your connection at other hours of the day and contact your ISP directly if you believe this is causing the connection issue.
There are several ISPs which block ports required for the proper operation of Steam and Steam games:
• 012.net (Steam traffic blocked)
• Bluewin (Firewall blocks Steam from provider side - must be disabled through provider's service portal)
• Dutch Telecom (Steam traffic blocked)
• ISPFree (Steam traffic blocked)
• Micronet Broadband (Steam traffic blocked)