user17301: For most openings that I play (e4 and d4 openings) I have observed that they take exactly 4 moves (e.g. Giuoco Piano Game without variation). 
C50: Giuoco Pianissimo, Italian four knights variation takes 5 moves. 
The Van't Kruijs Opening (1. e3) takes less than 1. 
Which opening requires the longest amount of chess moves?
Edit
As I see I have been unclear, let me clarify. When I say two distinct openings, all I mean is a different name. For example, Ruy Loypez, XXX Variation is different from Ruy Lopez Ppening is different from Ruy Lopez, YYY Variation. 

user12523: Here is one possible answer: there is an eco.json file available which is based on the Encyclopedia of Chess Openings. If you take the contents of that file and sort the openings by the length of the line leading to the named position, there is a unique winner, the 36 plies long Ruy Lopez: Marshall, Main Line, Spassky Variation:
{'c': 'C89',
 'f': '5rk1/5ppp/p1pbr3/1p1n3q/P2P2b1/1BPQB1P1/1P1N1P1P/R3R1K1 w -',
 'id': 3320,
 'm': 'e2e4 e7e5 g1f3 b8c6 f1b5 a7a6 b5a4 g8f6 e1g1 f8e7 f1e1 b7b5 a4b3 e8g8 c2c3 d7d5 e4d5 f6d5 f3e5 c6e5 e1e5 c7c6 d2d4 e7d6 e5e1 d8h4 g2g3 h4h3 c1e3 c8g4 d1d3 a8e8 b1d2 e8e6 a2a4 h3h5',
 'n': 'Ruy Lopez: Marshall, Main Line, Spassky Variation'}


17301: <p>For most openings that I play (e4 and d4 openings) I have observed that they take exactly 4 moves (e.g. Giuoco Piano Game without variation). </p>

<p>C50: Giuoco Pianissimo, Italian four knights variation takes 5 moves. 
The Van't Kruijs Opening (1. e3) takes less than 1. </p>

<p>Which opening requires the longest amount of chess moves?</p>

<h2>Edit</h2>

<p>As I see I have been unclear, let me clarify. When I say two distinct openings, all I mean is a different name. For example, Ruy Loypez, XXX Variation is different from Ruy Lopez Ppening is different from Ruy Lopez, YYY Variation. </p>
 12523: <p>Here is one possible answer: there is an <a href="https://github.com/niklasf/eco" rel="noreferrer">eco.json</a> file available which is based on the <em>Encyclopedia of Chess Openings</em>. If you take the contents of that file and sort the openings by the length of the line leading to the named position, there is a unique winner, the 36 plies long <em>Ruy Lopez: Marshall, Main Line, Spassky Variation</em>:</p>

<pre><code>{'c': 'C89',
 'f': '5rk1/5ppp/p1pbr3/1p1n3q/P2P2b1/1BPQB1P1/1P1N1P1P/R3R1K1 w -',
 'id': 3320,
 'm': 'e2e4 e7e5 g1f3 b8c6 f1b5 a7a6 b5a4 g8f6 e1g1 f8e7 f1e1 b7b5 a4b3 e8g8 c2c3 d7d5 e4d5 f6d5 f3e5 c6e5 e1e5 c7c6 d2d4 e7d6 e5e1 d8h4 g2g3 h4h3 c1e3 c8g4 d1d3 a8e8 b1d2 e8e6 a2a4 h3h5',
 'n': 'Ruy Lopez: Marshall, Main Line, Spassky Variation'}
</code></pre>
