Is there a maximum length requirement for 3/4" liquidtight flexible nonmetallic conduit type-B?
You can install Liquidtight Flexible Nonmetallic Conduit (LFNC) in lengths longer than 6' (1.8m), but only if it is securely fastened at intervals less than 3' (900 mm), and within 12&quot; (300 mm) of boxes and fittings.

Update.
Turns out that if you're following NEC 2011, 680.42(A)(1) limits you to 6' of LFNC for hot tubs. The 2014 version of the code, seems to have removed that restriction.

National Electrical Code 2014
Chapter 3 Wiring Methods
Article 356 Liquidtight Flexible Nonmetallic Conduit: Type LFNC
356.10 Uses Permitted. LFNC shall be permitted to be used in exposed or concealed locations for the following purposes:
(5) Type LFNC-B shall be permitted to be installed in lengths longer than 1.8 m (6 ft) where secured in accordance with 356.30.
356.30 Securing and Supporting. Type LFNC-B shall be securely fastened and supported in accordance with one of the following:
(1) Where installed in lengths exceeding 1.8 m (6 ft), the conduit shall be securely fastened at intervals not exceeding 900 mm (3 ft) and within 300 mm (12 in.) on each side of every outlet box, junction box, cabinet, or fitting.
National Electrical Code 2014
Chapter 6 Special Equipment
Article 680 Swimming Pools, Fountains and Similar Installations
680.42 Outdoor Installations. A spa or hot tub installed outdoors shall comply with the provisions of Parts I and II of this article, except as permitted in 680.42(A) and (B), that would otherwise apply to pools installed outdoors.
(A) Flexible Connections. Listed packaged spa or hot tub equipment assemblies or self-contained spas or hot tubs utilizing a factory-installed or assembled control panel or panelboard shall be permitted to use flexible connections as covered in 680.42(A)(1) and (A)(2).
(1) Flexible Conduit. Liquidtight flexible metal conduit or liquidtight flexible nonmetallic conduit shall be permitted.



National Electrical Code 2011
Chapter 6 Special Equipment
Article 680 Swimming Pools, Fountains and Similar Installations
680.42 Outdoor Installations.
(A) Flexible Connections.
(1) Flexible Conduit. Liquidtight flexible metal conduit or liquidtight flexible nonmetallic conduit shall be permitted in lengths of not more than 1.8 m (6 ft) external to the spa or hot tub enclosure in addition to the length needed within the enclosure to make the electrical connection.