Update - Having discussed the subject with my colleagues at Kwiziq and with some teachers in France, I reiterate that for the majority of France, the 'devrai' and 'devrais' will be pronounced exactly the same.
Take a look at a reference to a study included in this link (an awful load of adverts but the map is particularly relevant ).
Now that doesn't mean that the 'ai/ais' will not be pronounced differently in different parts of the country.
e.g. in the south of France, it will be an -é of bébé for both, in la région parisienne it will be the è of 'lait'.
The importance here to go back to Laurie's original question is how to make sure you convey the right meaning and this is what happens in practice -
We tend to avoid using 'devrai' in the future and use for instance 'falloir' :
Il faudra que je parte à 14 heures = I will have to leave at 2 pm
or
Il va falloir que je parte ...= I am going to have to leave ...
or even -
on devra se quitter à 14 h
Here, by changing the pronoun you eliminate the problem/ confusion which is with only the first person singular je.
Unfortunately, the verb 'falloir' is followed by the subjunctive, but this is preferable to confusion.
Hope this satisfies everybody, good conversation!