hi,

it is nice that you showed us the data! The first, obvious, question is about the goal of the analysis: do you just want to prove the relationship between temp and duration or do you want to build a predictive model?

Second: there seem to be two issues with your data : if this is in time order then you have a strong grouping (high temps only in a short period) and you can not exclude any confounding factors, like something else besides temps being also different at the time of the measurement. Also you have a large gap in the temperatures between about 15 and 22. Obviously for predictions this will be problematic.

If you only want a generic proof that higher temps are linked to lower durations, you could for instance group the temperatures in 3 classes - High, Med, Low and run an ANOVA or some non-parametric variant (like Kruskal-Wallis). You have enough data so that the lower power of the non-parametric test will not matter, the effect is also quite clear.

If you want predictions you should take care of that gap first IMO.

regards