Since you don't have enough knowledge about investing in Bitcoin, do enough research and gather a lot of knowledge about investing before you invest. Everything you need to know about your investment. And before investing first prepare yourself for full investment. If you get a salary of $300 per month, if you invest $50 in bitcoins out of that, you can very well serve your family and all your personal expenses with $250. You don't need any exact time to buy bitcoins, if you invest in long term you will definitely get profit. Just invest for long term. If you continue to invest in Bitcoin in this way, you will surely achieve great success in life.
And good luck to you
Of course OP needs to invest for long term also he needs to grow the investment by investing in DCA method. Whenever OP invests in DCA method he has to hold the investment for long term. Here is OP's monthly income of $300, there is $250 for his household expenses and $50 to invest in Bitcoin. 50$ monthly investment is not bad. If he can invest regularly 50$ in Bitcoin and keep it for a long time then he will get big returns.
50 dollars monthly is not that bad specially if you know which coin you are investing (this means altcoin of course) but if you are confident about Bitcoin to bring you better result for that amount then yeah put that 50 bucks in bitcoin monthly and that would be 600$ a year, that for me is too small talking about how pricey bitcoin nowadays.
but this is for OP to decide, he has His strategy and we are just giving Him second option and better understanding about things in life.