Does Drying The Right Foot Before Washing The Left Invalidate Wudu?

Continuity in Wudu means not to delay washing one part until the one before it has dried within a moderate amount of time. Therefore, if the part dries because of intense heat, wind, or by drying it with a towel, this has no effect (on Wudu), if washing the part is not delayed longer than the time it normally takes for the part before it to dry; what matters is that it should not take longer than that.

Some of the scholars defined continuity as, not waiting too long between the washing of various parts of the body, as defined by custom, and they did not connect it to the time it takes for them to dry. 

Ibn Qudamah (may Allah have mercy on him) said in Al-Mughni (1/181): 

“The continuity that is required is that one should not leave washing another part of the body until enough time has elapsed for the previous part to dry within a moderate amount of time, because a part may dry at times faster than others.”

It says in Kashf Al-Qina` (1/105): 

“Continuity means that one does not delay washing one part until after the part before it has dried at a time when it is neither too hot nor too cold. So one does not delay washing the hands until the face has dried, or delay wiping the head until the hands have dried, or washing the feet until the head has dried if it is washed. From this it may be known that if a person delays wiping the head until his face has dried but not his hands, that does not matter.”

Based on this, if a person washes his right foot then dries it, then he washes his left foot without taking as much time as it would ordinarily take for it to dry by itself, then his Wudu is valid. 

And Allah knows best.