I've been attending weekend classical time control tournaments (usually 90 minutes with a 30 second increment) for the last year or so.
Four games in one day is challenging and will be tiring for you mentally even if you were experienced.
There is a big difference between 15:15 and 45:5. If you assume and plan for a 40 move game then you're shifting from spending an average of 24 seconds per move to an average of 72 seconds per move. Most importantly, so is your opponent which means you'll need a much greater focus on finding the best moves. No one or two move threats that weaken your position if defended against, because your opponent will spot them with a longer time control. Five-seconds is also a low increment, so you do need to monitor your clock more than you would with a 15 second increment because you can't count on finding good moves in 5 seconds or building your time back up.
I'd strongly recommend you play some online games at that time control before the tournament. You really need to know and have a feel for how long that is. You'll almost certainly bias to thinking you have less time than you do. Slow your game right down. 45 minutes is a long time when you also include thinking on your opponents moves.
You will also need to handle set backs and poor games. I don't know where you'll be relative to your opponents in strength but if you're playing four matches it's likely you'll make some moves you're not happy with you and are likely to lose games. You'll need to manage your expectations pre-tournament and your reaction to this. I've experienced being 'shell shocked' after a horrendous blunder in one game and going on to lose other games that I shouldn't have because I couldn't get it out of my head. Treat each game individually, try to focus on finding the best moves and as much as possible detach yourself from the result and outcome of the game. It's fine to lose if you played well. That's easier said than done.
Do you have prior experience OTB (at a club?) or will this be your first OTB play as well as first tournament play? There is potentially other additional advice you'd benefit from if it's your first OTB game.
Hey all, I'm about to go to my first tournament in April, and it's a 4 game in a row tournament for one day, with a 45 minute time per side and 5 second delay. I've been rehearsing my openings and watching streams from the Sinquefield cup, but the longest game I've ever played was a 15|15 minute game and a lot of blitz. I'm worried that I won't know what to do once I'm beside a clock or how to conduct myself or what to think, even. Truth be told, I'm nervous and I shouldn't be, but is there anyone that can share some of their experience playing in OTB tournaments and how they thought about their positions while they played?