At SZX, stay airside—modern terminal with solid food options, and border/security checks add risk if exiting.
With 144-hour TWOV clearance, take Metro Line 11 from the airport to Qianhai or Nanshan Station in about 30 minutes (CNY 7). The Houhai waterfront area and Nanshan commercial district are 15 minutes walk from Qianhai Bay Station. Skip any site that requires a tour or booking. Allow 80 minutes for the full round-trip metro ride and give yourself a 2-hour departure buffer.
Futian CBD or OCT (Overseas Chinese Town) are the top options. From the airport, Metro Line 11 to Convention Center Station takes 40 minutes (CNY 8). OCT Loft is an arts and design district worth 90 minutes. For shopping, MixC Shenzhen Bay or ShenZhen Bay Park are 10 minutes by taxi from Houhai Station. Lunch options around OCT average CNY 50 to 80 ($7 to $11).
High-speed rail from Futian Station to West Kowloon (Hong Kong) takes 22 minutes and costs CNY 210 ($29). You need a valid Hong Kong entry permit. If you qualify, a half-day in Tsim Sha Tsui or Victoria Harbour is a strong option before returning. Otherwise, Shenzhen's Dafen Oil Painting Village (art replica district) and Lianhuashan Park fill an additional 3 hours without leaving China.