I never used hourglasses because I feared out-decking. And I'm missing the Eternity so that's also a pain in the arse trying to get.
This was a mistake I made when I started a rainbow.
When he says to add 4 hourglasses, don't plan on playing all four. You only have that many to increase your chances of drawing one early (they are useless during the endgame). You should only be using one, or maybe two of them. The other two can be used to replace one that is destroyed or stolen, or used as a decoy against the AI (so it targets the hourglass to destroy rather than your weapon or shield). Do a crude calculation on how many turns it's going to take to kill your opponent and stop drawing 3-5+ cards before that (to account for an unexpected heal, etc.). If you have all your creatures out and have control of the board, you can stop drawing earlier. The hourglass is just there to speed things up a bit, since normally you have to stall while you get everything out.
Also, if you plan to play rainbows or any decks with time over 35 cards, make the hourglasses a priority upgrade. Since you want to play them as early as possible, the cheaper cost is critical.