It'll work with gentle heat - about 50°C - and stirring. Might take a while, couple hours. I'd heat it for maybe ten of that, use a water bath, but keep the water out of the PG! You'd find a 1-mg/mL solution easier and quicker to prepare. Benzos are soluble in PG, bit not like HCl salts of other drugs into water, which is usually very quick and can often be done at much higher concentrations.
TL: Sandard benzo information in the name of HR, most people, perhaps the OP have read this many times, it bears repeating:
Someone will mention you could prepare a 10-mg/mL solution, and you can, but if you have the PG, I suggest a more dilute solution for HR and practice reasons. Just be certain your balance ('scale') is accurate and precise to no more than 1mg, +/-0.5mg error! At that weighing 100-mg or even 50-mg should be pretty accurate.
Warning though: If it's only you using that 250-mg it should last you years. Keep it cool and out of light. Even at that maybe not make up a full 250-mg. That's a lot. More then you need for several months if it's just you and a few friends. Be very, vary wary of giving this to other people, you don't want to be responsible for the blackout actions of someone else.
Benzos are no joke. You've probably seen and read the warnings. I'd keep dosing as low as possible and not more than once a week. If you can't keep to a rigid schedule of when, how and why you use benzos - stop. You have a problem to sort out.
Same goes for using benzos to come off drugs that hype you up. Infrequent, low dose. You'll be glad you kept it at that. The people I know who get the most out of benzos long term use them sparingly and at as low a dose as possible. One friend is going on over a decade enjoying a 1-mg clonazepam every now and then and to come off acid trips. I truly envy him.
Benzos are very useful for a limited number of ailments and a poor drug to try to get subjective effects that are pleasant without running into trouble both acute and chronic. Chronic issues with benzos are terrible. Life threatening, life depleting withdrawal that is protracted much longer than you'd think - upto forever, often years long, even in cases of rather short dependencies of a year or so.
Yes, I know etizolam is a thienodiazepine. It's all the same pharmacologically in most significant respects. As far as has been studied.
End of duplicitous benzo HR speech.
Edits: grammar, tweaks
